GENERAL   SCIENCE 

FIRST  COURSE 


BY 

LEWIS   ELHUFF,   A.M.    (YALE) 

INSTRUCTOR  IN   SCIENCE   IN   THE    GEORGE   WESTINGHOUSE 
HIGH   SCHOOL,   PITTSBURGH,   PA. 


D.   C.   HEATH   &   CO.,   PUBLISHERS 

BOSTON  NEW  YORK  CHICAGO 


COPYRIGHT,  1916, 
BY  D.  C.  HEATH  &  Co. 

IH6 


PREFACE 

THIS  book  is  intended  to  offer  a  scientific  explanation  for 
the  many  and  varied  experiences  which  pupils  of  high  school 
age  have  had  and  to  create  a  desire  for  further  knowledge  of 
scientific  subjects.  There  is  a  growing  desire  among  science 
teachers  to  have  a  general  introductory  course  in  which  the 
fundamental  principles  of  science  and  of  scientific  study  are 
presented  in  such  a  way  that  pupils  will  acquire  the  desire  for 
a  systematic  study  of  the  special  branches  of  science.  There 
are  also  many  high  schools  in  which  only  a  year  or  so  can  be 
devoted  to  the  subject  of  science.  In  these  a  general  course 
giving  an  explanation  of  the  pupils'  experiences  with  sugges- 
tions of  how  to  acquire  further  information  will  be  most  val- 
uable. In  many  city  high  schools  a  number  of  courses  are 
offered  in  which  no  science  subject  is  required.  Many  of  the 
larger  cities  are  now  adding  a  half-year  of  general  science  to 
these  courses  in  which  special  science  subjects  are  not  required, 
thus  giving  such  pupils  —  as  in  the  commercial  courses  —  an 
understanding  of  every-day  phenomena  and  some  idea  of  the 
laws  of  health.  This  book  is  intended  to  meet  these  various 
needs. 

After  having  taught  various  phases  of  science,  including 
General  Science,  for  several  years  and  having  experimented  on 
the  order  of  arrangement  of  the  subject-matter  and  the  method 
of  presentation,  the  author  has  concluded  that  the  arrangement 
of  the  material  as  presented  in  this  book  is  most  effective  in 
securing  the  following  results: 

First.  A  desire  to  grow  strong  in  body  and  mind  and  to 
remain  free  from  disease  and  to  avoid  the  use  of  stimulants 
and  narcotics  is  created.  Successful  work  on  the  part  of  many 
boys  and  girls  is  dependent  upon  this  desire  becoming  strong 

359393 


iv  PREFACE 

enough  to  rule  the  body.  This  desire  will  be  created  by  the 
material  in  the  first  few  chapters  if  the  teacher  is  of  the  proper 
character.  Enough  material  is  presented  to  give  the  pupils 
sufficient  knowledge  and  wisdom  so  that  they  may  know  how 
to  protect  themselves. 

Second.  A  logical  method  of  thinking  is  developed,  so  that 
the  pupils  have  a  mind  open  for  the  consideration  of  new  facts 
and  principles,  thus  relieving  them  of  some  of  their  supersti- 
tions. Pupils  who  are  taught  in  a  logical  manner  soon  form 
logical  habits  of  thinking  and  become  able  to  judge  with  an 
accuracy  that  will  surprise  many  teachers. 

Third.  A  desire  for  more  knowledge  and  further  scientific 
study  is  created.  The  fundamental  principles  underlying  scien- 
tific knowledge  are  gradually  developed  and  appear  in  new  forms 
in  various  places  with  new  applications.  There  are  sufficient 
repetitions  of  the  fundamental  facts  to  make  the  learner  thor- 
oughly familiar  with  them  so  that  he  can  use  them,  thus  giving 
him  confidence  in  himself.  Self-confidence  of  the  right  sort  is 
an  absolute  necessity  on  the  part  of  a  learner.  The  author  would 
like  to  suggest  that  teachers  give  a  review  at  the  close  of  each 
long  chapter  and  also  at  the  close  of  a  number  of  chapters  on 
related  material.  Repetition  of  fundamentals  until  they  actually 
become  a  part  of  the  pupil  is  a  secret  of  successful  science  teaching. 

The  material  which  touches  upon  the  pupils'  personal  habits 
is  placed  as  early  as  possible  in  this  course,  so  that  they  can 
use  it  at  the  beginning  of  their  high  school  course  and  form 
proper  hygienic  habits  before  the  four  years  are  passed.  The 
elementary  chemistry  is  placed  early  in  the  course  in  order  that 
a  better  understanding  of  the  following  matter  may  be  had. 
In  connection  with  chemistry  it  is  not  difficult  to  get  an  idea 
of  an  atom  and  a  molecule.  These  ideas  are  fundamental  to 
the  study  of  all  scientific  subjects  and  are  necessary  for  a  respec- 
table understanding  of  the  chapters  that  follow  A  few  chemi- 
cal symbols  have  been  introduced  to  give  the  pupils  an  idea  of 
the  composition  of  matter.  Most  pupils  have  a  desire  to  know 
the  symbols  of  many  common  substances.  Sufficient  material 


PREFACE  v 

and  explanation  are  given  both  in  the  text  and  in  the  glossary 
for  the  complete  understanding  of  technical  terms  used  in  this 
course. 

When  only  a  half-year  is  devoted  to  General  Science  the 
author  suggests  that  the  order  of  the  book  be  followed  to  the 
end  of  Chapter  XXIV  and  then  if  more  time  remains  the  teacher 
can  select  from  the  remaining  subjects  what  will  be  most  useful 
to  the  pupils.  It  is  hardly  possible  to  cover  the  entire  book  in 
a  half  year's  work  so  that  the  pupils  will  get  a  definite  and  last- 
ing impression  of  the  principles  underlying  the  subject-matter. 

The  field  covered  in  this  course  may  at  first  sight  seem  broad 
and  varied,  but  there  are  two  or  three  basic  ideas  which  have 
a  broad  application  and  which  the  mass  of  simple  facts  helps 
to  develop  into  clear  concepts.  These  basic  ideas  are  matter, 
its  properties,  and  how  matter  affects  other  matter,  —  the  re- 
action of  matter  upon  matter;  and  energy  as  a  property  of 
matter.  Pupils  should  be  required  to  draw  generalizations 
from  known  facts  wherever  possible.  The  general  ideas  thus 
acquired  will  remain  with  the  pupils,  although  many  of  the 
details  may  be  forgotten.  If  no  generalizations  are  acquired, 
the  pupil's  mind  will  be  blank  after  the  details  have  evaporated. 
The  pupils  who  have  detailed  facts  continuously  heaped  upon 
them  without  general  truths  leave  our  educational  institutions 
uneducated.  They  are  the  ones  who  may  recall  that  they 
studied  a  certain  subject  while  in  school,  but  not  much  more. 
Many  detailed  facts  will  remain  with  a  general  truth  through 
the  process  of  mental  association. 

The  author  would  suggest  that  this  book  is  in  no  case  intended 
to  take  the  place  of  the  live  teacher.  It  is  intended  to  furnish 
material  and  suggestions  for  class  discussion  and  to  stimulate 
the  minds  of  pupils  so  that  they  may  think  about  their  experi- 
ences and  acquire  more.  There  are  in  the  course  some  sug- 
gestions which  will  cause  pupils  to  reflect  on  the  past  history 
of  man  and  to  seek  for  the  new  in  the  present  and  future.  The 
illustrations,  drawings  and  photographs,  are  given  in  series 
wherever  possible,  so  that  a  more  definite  idea  may  be  acquired, 


vi  PREFACE 

and  in  order  to  lead  to  reading  in  other  books  which  give  more 
details. 

The  author  wishes  to  express  his  appreciation  to  the  class 
of  1917  of  the  George  Westinghouse  High  School  for  the 
inspiration  received  from  them  to  start  this  book;  to  Misses 
C.  E.  Kim  and  Elizabeth  Collett  for  suggestions  in  English; 
to  his  wife  and  others  for  reading  the  proof;  to  the  United 
States  Department  of  Agriculture,  the  Westinghouse  Motor 
Company,  LaFlam  Milk  Co.,  and  Mr.  Roe  for  photographs 
to  illustrate  the  work. 


CONTENTS 

CHAPTER  PAGE 

I.  INTRODUCTION i 

II.  HEALTH 5 

III.  CHEMISTRY  OF  COMMON  THINGS 9 

IV.  CHEMISTRY  OF  BAKING 23 

V.  PRESERVATIVES  AND  DISINFECTANTS 31 

VI.  HABIT-FORMING  AGENTS     40 

VII.  OXYGEN  AND  OXIDATION 47 

VIII.  CARBON  DIOXIDE 53 

DC.  BREATHING  AND  VENTILATION 59 

X.  MATTER  AND  ENERGY 64 

XL  HEAT  : 71 

XII.  HEAT  OF  VAPORIZATION     84 

XIII.  HEAT  OF  FUSION  AND  DISSOLUTION 92 

XIV.  HEATING  BUILDINGS 95 

XV.  FOOD 112 

XVI.  WATER 134 

XVII.  THE  AIR 145 

XVIII.  SOME  PROPERTIES  OF  GASES 163 

XIX.  SIMPLE  MACHINES 174 

XX.  WATER  WHEELS  AND  WINDMILLS 199 

XXI.  STEAM  AND  GAS  ENGINES 207 

XXII.  WATER  OR  LIQUID  PUMPS      213 

XXIII.  GAS  PUMPS 221 

XXIV.  CITY  WATER  SUPPLY 225 

XXV.  MAGNETS 237 

XXVI.  SIMPLE  ELECTRICAL  APPLIANCES  AND  MACHINES.  248 

XXVII.  LIGHT 272 

XXVIII.  THE  HUMAN  EYE 279 

XXIX.  ARTIFICIAL  LIGHT 289 


viii  CONTENTS 

XXX.   SOUND 294 

XXXI.  VOCAL  CORDS  AND  THE  EARS 300 

XXXII.  THE  SOIL 305 

XXXIII.  How  TO  CARE  FOR  SOIL 321 

XXXIV.  How  PLANTS  GROW 335 

XXXV.  How  PLANTS  ARE  PROPAGATED 352 

XXXVI.   USE  OF  PLANTS  TO  MAN 361 

XXXVII.  Low  FORMS  OF  PLANT  LIFE 368 

XXXVIII.   PLANT  DISEASES  AND  PESTS 373 

XXXIX.  THE  ANIMAL  SERIES 381 

XL.  ANIMALS  AS  DISEASE  CARRIERS 396 

XLI.   MAN'S  PLACE  IN  NATURE 404 

XLII.  THE  EARTH  AND  ITS  NEIGHBORS 407 

APPENDIX  —  The  Metric  System 415 

GLOSSARY 419 

SUGGESTIONS  TO  TEACHERS 425 

INDEX 429 


GENERAL    SCIENCE 

CHAPTER  I 
INTRODUCTION 

Why  Study  Science?  —  This  is  an  age  of  scientific 
research  and  experiment.  Science  is  improving  every 
kind  of  industry  upon  which  man  depends  for  his  physical 
existence.  In  many  important  ways  our  modern  civi- 
lization is  different  from  that  of  our  great-grandfathers. 
This  improvement  has  been  made  possible  by  the  results 
obtained  from  scientific  investigations  carried  on  by 
men  who  have  devoted  their  lives  to  the  work. 

Scientists  have  improved  the  means  of  travel  many- 
fold  during  the  past  fifty  years.  To  them  we  give  the 
credit  for  our  modern  railroads,  electric  lines,  swift  ocean 
steamers,  airships,  aeroplanes,  automobiles,  and  various 
mechanical  devices  for  making  excavations  and  recon- 
structions —  all  in  the  mechanical  realm. 

In  the  field  of  science  that  concerns  life  —  that  is,  in 
the  field  of  biology  —  great  discoveries  have  been  made 
concerning  plant  and  animal  life  processes,  the  physical 
structure  of  plants  and  animals,  and  the  dependence  of 
man  upon  microscopic  plant  forms.  Men  have  dis- 
covered many  of  the  microscopic  plant  forms  and  animal 
organisms  which  produce  disease  and  have  learned  how 
to  destroy  these  one-celled  enemies  of  man.  Man  could 


2  GENERAL    SCIENCE 

not  live  in  modern  conditions  without  his  knowledge  of 
disease  germs  and  how  to  eradicate  them. 

The  investigations  and  experiments  in  agriculture 
have  improved  the  farming  and  stock-raising  industries 
so  that  a  sufficient  quantity  of  food  can  be  produced. 
Experiments  in  animal  feeding  have  led  to  the  con- 
sideration of  human  feeding  and  the  analysis  of  human 
foods. 

To  live  without  some  knowledge  of  the  general  princi- 
ples of  science  is  like  feeling  one's  way  in  the  dark.  To 
study  science  is  to  learn  how  to  understand  the  environ- 
ment in  which  we  live  and  how  to  adjust  ourselves  to 
it  and  how  to  improve  our  physical  and  social  condi- 
tion. To  study  science  is  to  learn  the  basic  principles  of 
morality. 

The  important  thing  for  boys  and  girls  of  high  school 
age  is  to  learn  how  to  take  proper  care  of  their  physical 
bodies  so  they  may  grow  to  maturity  with  good  health 
and  with  a  well-developed  brain  and  nervous  system. 
Boys  and  girls  cannot  accomplish  very  much  even  in 
high  school  unless  they  learn  how  to  take  proper  care  of 
themselves  and  how  to  adjust  themselves  to  their  envi- 
ronment.1 Pupils  know  that  they  accomplish  their  work 
with  difficulty  when  they  have  a  cold,  headache,  or 
indigestion.  The  pleasantness  of  school  work  depends 
upon  continuous  effort  and  a  knowledge  of  how  to  keep 
free  from  disease.  If  in  the  first  part  of  this  course  an 
effort  is  made  to  apply  the  general  principles  to  your 
daily  life,  your  school  work  will  not  become  a  burden 
but  a  pleasure. 

Then  why  study  science? 

The  answer  is:    To  learn  how  to  live. 

1  See  Glossary  for  words  that  may  seem  difficult  to  understand. 


INTRODUCTION 


MADAME     CURIE,     of      the    Uni-  Copyright  by  Underwood  &  Underwood 

versity  of   Paris,   who    discovered  GUGLIELMO    MARCONI,  who    in- 

radium.  vented  wireless  telegraphy. 


EDWARD  JENNER,     who     about  Louis  PASTEUR,  who  discovered 

1800  discovered  a  method  of  pre-      the  germs  of  many  contagious  dis- 
venting  smallpox  by  vaccination.          eases  and  how  to  kill  them. 

SOME  OF  THOSE  WHO  HAVE  MADE  USEFUL  DISCOVERIES 


4  GENERAL  SCIENCE 

One  definition  of  science  is:  Science  consists  of  systemat- 
ically arranged  knowledge  resulting  from  careful  and  pur- 
poseful observation. 

There  are  many  experiences  that  pupils  of  high  school 
age  have  gathered  at  random,  for  which  the  subject- 
matter  in  this  course  will  offer  an  explanation.  Our 
coming  lessons  will  classify  the  knowledge  gained  by 
accidental  experiment  and  observation,  and  thus  form 
a  basis  for  future  observation  and  study,  either  in  or 
out  of  school. 

QUESTIONS   AND  EXERCISES 

1.  Make  a  list  of  the  inventors  about  whom  you  know  some- 
thing.    Name  the  most  important  things  each  one  invented,  giving 
the  approximate  date. 

2.  Make  a  list  of  those  who    have  made  important  scientific 
discoveries. 

3.  Name  all  of  the  things  at  home  which  have  recently  come 
into  use. 

4.  Make  a  list  of  the  things  used  in  your  locality  which  were  not 
thought  of  when  your  grandparents  were  young. 


CHAPTER   II 
HEALTH 

1.  Meaning  of  Health.  —  When  we  notice  the  stream 
on  the  hillside,  and  the  many  plants  and  animals  about 
us  in  the  cities  and  country,  we  find  that  everything  is 
busy  and  active.     To  have  good  health  is  to  be  active, 
ready  for  work.     To  have  good  health  is  to  be  happy 
and  pleasant,  to  have  no  aches  or  pains  to  disturb  one's 
activity  and  work.    Would  you  not  like  to  be  in  a  high 
school  where  all  the  boys  and  girls  have  good  health  and 
never  have  to  stay  at  home  because  of  sickness? 

2.  Value    of    Health.  —  Health    is   wealth.     But    the 
joy  and  happiness  which  come  to  the  home  where  there 
is  no  sickness  cannot  be  measured  in  dollars  and  cents. 
If  a  workman  earning  twenty-five  dollars  a  week  gets 
sick  and  is  confined  to  his  home  for  two  weeks,  what  is 
the  cost?     Services  of  the  physician,  $20.00;    medicine, 
$5.00;    nurse,  $12.00;    extra  work  for  his  wife,  $10.00; 
loss  in  wages,  $50.00;    making  a  total  loss,  for  the  two 
weeks,  of  $97.00  in  money,  besides  the  sorrow  and  suffer- 
ing in  that  home.     Millions  of  dollars  are  wasted  every 
year  because  people  are  careless  about  their  health. 

3.  School  Work  and  Health. —  Boys  and  girls  cannot 
do  good  work  in  school  unless  they  are  healthy  and  know 
how  to  keep  healthy.     When  you  feel  sleepy  because  of 
overwork  or  because  of  staying  up  too  late  at  night, 
you  cannot  do  good  school  work,    Your  brain  is  not  at 


6  GENERAL  SCIENCE 

its  best  under  such  conditions.  Headaches,  bad  colds, 
and  indigestion  hinder  study  and  success  in  school  work. 
So  do  not  do  the  things  that  cause  these  troubles.  Many 
boys  and  girls  have  to  leave  school  because  of  bad  health 
which  is  often  due  to  lack  of  knowledge  of  the  laws  of 
health  and  carelessness  on  the  part  of  the  parents  and 
the  pupils  themselves. 

4.  Success    and    Health.  —  Success    in    life    depends 
largely    upon    health.     Health    depends    upon    habits. 
Habits  are  formed  in  youth.     Health  is  to  the  future 
man  what  the  roots  are  to  a  tree.     The  foundation  for 
much  of  their  illness  or  health  in  later  life  is  laid  by 
the  boys  and  girls  while  in  school.    That  instruction  which 
helps  pupils  to  understand  the  care  of  the  body,  and  the 
value  of  fresh  air,  proper  food,  exercise,  and  cleanliness, 
will  add  much  to  the  wealth  of  the  nation  and  the  future 
happiness  of  its  people. 

5.  Air  and  Health.  —  Keep  out  of  doors  as  much  as 
possible.     Breathe   through   the  nose,   not   through   the 
mouth.     Have  your  living  rooms  well  ventilated.     Not 
only  purity,  but   also  coolness,  dryness,  and  movement 
of  the  air,  without  a  draft,  are  advantageous.     Air  in 
heated  houses  in  winter  is  usually  too  dry  and  may  be 
moistened  by  having  a  small  vessel  of  water  somewhere 
on  the  heater.     The  minimum  clothing  that  will  keep 
one  warm  is  the  best.     The  more  porous  the  clothes, 
the  more  the  skin  is  educated  to  perform  its  purpose  with 
increasingly  less  need  for  protection.     Take  an  air  bath 
as  long  and  often  as  possible. 

6.  Water   and   Health.  —  Take   a   daily   water  bath, 
not  for  cleanliness  alone,  but  for  skin  gymnastics.     A 
cold  bath  is  good,  but  a  short  hot  bath  followed  by  a 
short  cold  one   is  better.     To   rest   the  nerves,  take  a 


HEALTH  7 

neutral  bath,  beginning  with  the  water  at  98°  F.,  and 
allowing  it  to  cool  not  more  than  5°  F.;  continue  this  bath 
for  15  minutes  or  more.  Be  sure  that  the  drinking  water 
is  free  from  dangerous  germs  and  impurities.  Ice  water 
should  be  avoided,  especially  during  hot  weather.  Cool 
water,  about  one-half  pint  taken  half  an  hour  before 
breakfast  and  when  retiring,  is  a  remedy  for  constipation. 

7.  Food  and  Health.  —  Form  the  habit  of  masticating 
all  food  until  it  is  swallowed  without  conscious  effort. 
Give  as  much  attention  as  possible  to  the  taste  rather 
than  to  the  chewing.  Food  should  simply  be  chewed 
and  relished,  with  no  thought  of  swallowing.  There 
should  be  no  more  effort  to  prevent  than  to  force  swallow- 
ing. It  will  be  found  that  if  you  attend  only  to  the 
agreeable  task  of  extracting  the  flavors  of  your  food, 
nature  will  take  care  of  the  swallowing,  which  will  become 
involuntary  like  breathing.  Many  people  have  their 
habits  of  eating  and  appetite  perverted  by  hurry  and  by 
the  use  of  " abnormal"  foods.  The  best  results  from 
meals  can  be  secured  only  by  not  feeling  hurried  and  by 
taking  sufficient  time  for  thorough  mastication.  Liquid 
foods  should  be  mixed  with  saliva  before  swallowing. 

The  stomach,  like  any  other  part  of  the  body,  needs 
rest,  and  so  the  meals  should  be  far  enough  apart  to  grant 
time  for  this  rest.  The  stomach  can  digest  with  ease 
thoroughly  masticated  food.  Keep  your  stomach  clean 
by  not  allowing  anything  to  go  into  it  except  pure  food  and 
drink.  A  healthy  stomach  means  few  headaches  and 
very  few,  if  any,  diseases. 

QUESTIONS  AND  EXERCISES 

1.  Carefully  observe  in  your  school  whether  the  best  work  is 
done  by  the  boys  and  girls  who  are  healthy  or  by  those  who  are 
absent  often  because  of  sickness. 


8  GENERAL  SCIENCE 

2.  Make  a  list  of  the  successful  business  and  professional  men 
and  women  in  your  community  and  see  how  many  are  healthy  and 
how  many  are  sickly. 

3.  Make  a  careful  estimate  of  the  cost  of  the  last"  sickness  in 
your  own  home.     (See  §  2.) 

4.  What  is  your  conclusion  now  about  the  value  of  health? 

5.  Is  your  home  properly  ventilated?     Why? 

6.  Do  you  use  water  properly  for  drinking  and  bathing?     Why? 

7.  Do  you  use  the  right  kind  and  proper  amount  of  food?    Why? 


CHAPTER  III 
CHEMISTRY    OF    COMMON    THINGS 

8,  Chemistry  is  the  science  which  treats  of  the  composi- 
tion of  substances.  All  substances  are  made  up  of  very 
small  bodies  or  particles.  If  you  place  some  water  in  a 
vessel  on  a  hot  stove,  the  water  will  rapidly  escape  by 
evaporation.  How  does  it  get  out  of  the  vessel?  The 
water  on  the  road  or  sidewalk  soon  disappears  after  a 
summer  shower.  Where  does  it  go?  How  does  it  get 
away?  What  other  substances  can  be  made  to  evapo- 
rate? As  you  can  divide  a  quart  of  water  into  drops, 
so  you  can  divide  the  drops  into  smaller  bodies,  and  by 
the  use  of  heat  the  water  can  be  divided  into  such  tiny 
particles  that  they  can  fly  away  in 'the  air  and  not  be 
seen. 

You  can  take  a  piece  of  chalk  or  wood  or  coal  and 
divide  it  so  that  you  would  need  a  magnifying  glass 
or  microscope  to  see  the  smallest  parts.  But  the 
smallest  parts  are  still  chalk,  wood,  or  coal,  like  the 
large  piece  from  which  they  came.  If  you  hold  a  cold 
piece  of  iron  over  a  vessel  with  boiling  water  in  it, 
the  particles  of  water  escaping  will  collect  on  the  iron  in 
drops,  and  these  drops  will  be  water  the  same  as  that  in 
the  vessel.  This  shows  that  the  little  particles  escaping 
from  the  water  in  invisible  form  are  water.  These  little 
particles  of  water,  chalk,  and  coal  which  are  too  small  to 
be  seen  with  the  best  microscopes  are  called  molecules. 


io  GENERAL  SCIENCE 

9.  Molecules.  —  Molecules  are  the  smallest  divisions 
of  a  substance  that  have  the  same  properties  as  the  sub- 
stance itself.  The  small,  invisible  particles  that  escape 
when  water  is  heated  are  called  molecules  of  water. 
The  smallest  parts  of  chalk,  coal,  or  sugar  that  have  the 
properties  of  chalk,  coal,  or  sugar  are  also  molecules. 
Many  thousands  of  them  could  hang  on  the  point  of  a  pin. 

Why  do  these  molecules  escape  when  the  water  is 
heated?  —  If  a  dozen  boys  and  girls  were  standing  on  a 
platform  just  large  enough  to  hold  them,  they  could  all 
stay  on  as  long  as  they  did  not  move  around  too  much. 
But  however  quiet  they  might  try  to  be,  there  would  still 
be  some  movement,  though  perhaps  not  enough  to  shove 
them  out  of  their  position.  When  they  become  more 
active  and  begin  to  move  around  on  the  platform,  several 
may  have  to  jump  off.  The  more  active  they  get,  push- 
ing against  one  another,  the  smaller  the  number  that  can 
stay  on  the  platform,  and  in  time  only  one  may  bs  left. 

In  a  piece  of  ice  (a  solid)  the  molecules  can  move  out 
of  their  position,  but  not  far  —  not  even  far  enough  to 
change,  materially,  the  shape  of  the  ice.  When  heat  is 
applied  to  the  ice,  the  molecules  become  more  active,  and 
finally  they  shove  one  another  so  far  apart  that  the  ice 
loses  its  shape  and  becomes  a  liquid.  In  a  liquid  the  mole- 
cules move  around  so  freely  that  the  liquid  will  take  the 
shape  of  any  vessel  containing  it.  Since  molecules  of 
water  are  so  small  and  light  that  they  can  float  around  in 
the  air,  some  of  them  jump  out  of  the  liquid  into  the  air 
and  fly  away. 

The  process  by  which  molecules  continually  escape  from 
water  into  the  air  is  called  evaporation.  The  more 
heat  you  add  to  the  water,  the  faster  the  molecules 
move,  and  hence  they  escape  into  the  air  very  rapidly 


CHEMISTRY  OF  COMMON  THINGS  n 

when  the  water  is  boiling.  When  water  boils  steam  is 
formed.  Steam  consists  of  water  molecules  which  are 
moving  so  fast,  and  in  every  direction,  that  if  they 
should  bump  against  one  another  they  would  bounce 
apart  again  like  two  flying  baseballs.  If  they  should 
strike  a  wall  or  any  other  object,  the  molecules  would 
rebound  the  same  as  a  baseball  does  when  thrown 
against  an  object. 

The  molecules  composing  steam  are  free  to  move  in 
every  direction.  Steam  is  a  gas.  The  molecules  of 
gases  are  very  active.  If  illuminating  gas  is  turned  on 
in  the  house  without  lighting  it,  you  can  soon  smell  it 
because  the  molecules  spread  all  through  the  house. 
When  perfume  and  ammonia  bottles  are  opened,  some  of 
the  molecules  escape  and  travel  through  the  air  with 
great  speed.  They  can  easily  be  detected  by  the  smell. 

In  solids  the  molecules  move  slowly  and  within  a  very 
limited  space.  In  liquids  the  molecules  move  with  greater 
speed  than  in  solids,  and  they  move  around  and  over 
one  another  with  ease.  In  gases  the  molecules  move  with 
very  high  speed,  much  greater  than  in  liquids,  and  re- 
bound from  one  another  or  from  any  object  that  they  may 
strike. 

10.  Atoms.  —  Molecules  of  most  substances  such  as 
water,  sugar,  salt,  and  chalk  are  not  simple  molecules 
but  complex  ones.  These  complex  molecules  can  be 
divided  into  more  simple  forms.  But  when  the  water 
molecule  is  broken  up  into  its  more  simple  forms,  these 
simpler  forms  do  not  have  the  properties  of  water  as  the 
molecule  does.  The  same  is  true  of  all  other  complex 
molecules.  The  simpler  forms  do  not  have  the  same 
properties  as  the  molecules.  These  simpler  forms  or 
divisions  of-  the  complex  molecules  are  called  atoms,. 


12  GENERAL  SCIENCE 

When  a  substance  is  composed  of  atoms  which  are  all 
alike,  the  substance  is  said  to  be  a  simple  substance  or 
element,  such  as  iron,  gold,  lead,  silver,  oxygen,  hydrogen, 
sulphur.  When  a  substance  is  composed  of  molecules 
made  up  of  two  or  more  different  kinds  of  atoms,  it 
is  said  to  be  a  compound,  such  as  water,  salt,  sugar, 
chalk. 

Molecules  are  very  small,  but  atoms  are  smaller  than 
most  molecules,  as  many  molecules  are  made  up  of  two 
or  more  atoms.  A  molecule  of  common  salt  has  two 
atoms,  while  a  molecule  of  cane  sugar  has  45  atoms. 

In  ordinary  chemistry  the  atom  is  the  smallest  division 
that  can  be  made  of  any  substance.  So  the  atom  is  the 
smallest  chemical  unit.  The  kind  and  number  of  atoms 
that  are  used  to  make  a  molecule  determine  the  nature 
or  properties  of  the  molecule  and  hence  the  properties 
of  the  substance.  Most  substances  used  by  man  are 
composed  of  complex  molecules  and  so  they  are  called 
compounds.  These  compounds  are  classified  according  to 
their  own  properties  and  according  to  the  way  in  which 
they  affect  other  substances  or  compounds.  Most  of 
the  compounds  discussed  in  this  book  can  be  classed  as 
acids,  bases,  and  salts. 

11.  Acids.  —  Acids  occur  in  plants,  in  animals,  and 
in  the  earth.  Citric  acid  is  found  in  lemons  and  oranges 
and  gives  them  their  sour  taste.  It  can  be  prepared  from 
lemon  juice,  and  consists  of  beautiful  crystals  which 
will  easily  dissolve  in  water.  Malic  acid  is  present  in 
sour  apples.  Grapes  contain  tartaric  acid,  which  is 
used  in  making  cream  of  tartar  and  baking  powder. 
The  jack-in-the-pulpit  and  rhubarb  contain  oxalic  acid. 
Lactic  acid  is  formed  when  milk  sours.  Lactic  acid  is 
also  found  in  the  muscles  of  man  and  other  animals, 


CHEMISTRY  OF  COMMON  THINGS 


Vinegar,  which  is  made  mostly  from  apple  juice,  is  a 
dilute  solution  of  acetic  acid.  Hydrochloric  acid1  (HC1) 
is  formed  by  the  gastric  glands  of  the  human  stomach 
to  aid  in  digestion.  The  air  contains  small  amounts  of 
carbonic  acid  gas,  and  where  much  coal  is  burned  the 
air  contains  some  sulphur  dioxide.  Some  spring  waters 
contain  carbonic  acid,  while  soil  waters  contain  various 
acids  from  the  decay  of  plants  and  animals.  The  acids 
taken  from  plants  are  made  up  of  molecules  which  are 
very  complex.  Those  that  are  called  common  acids 
have  molecules  that  are  more  simple. 

The  chemical  symbols  for  acids,  as  well  as  for  other 
compounds,  show  the  number  of  the  atoms  in  the  mol- 
ecules. Some  common*  acids  are  hydrochloric 
acid  (HC1),  sulphuric  acid  (H2S04),  nitric  acid 
(HNO3),  and  acetic  acid  H(C2H3O2). 

Tests  for  acids.  —  Litmus  is  a  substance 
taken  from  the  group  of  plants  called  lichens. 
A  solution  is  made  of  the  litmus  coloring 
matter,  then  paper  that  has  been  prepared 
for  the  purpose  is  dipped  into  the  litmus 
solution  and  allowed  to  dry;  this  colored 
paper  is  called  litmus  paper.  The  common 
acids  and  nearly  all  other  acids  will  turn 
litmus  paper  from  blue  to  red. 

Very  dilute  solutions  of  the  common  acids 
taste  sour.  Fruit  acids  are  all  sour.  Sul- 


LlCHENS 

These  forms 
grow  on  rocks, 

phuric    acid    and   nitric   acid,  when    strong,   bark,    and 
will  make  a  brown  spot  on  wood,  paper,  or 
clothing,  and  will  also  injure  any  part  of  the  body  which 
they  touch.      For    this  reason   it  is  very  important  to 
learn   the   nature   and   properties   of   another   group   of 

1  See  Glossary,  under  heading  "Chemical  Symbols." 


I4  GENERAL   SCIENCE 

compounds,  called  bases,  which  will  neutralize  the  acids 
and  prevent  their  destructive  action. 

12.  Bases.  —  Bases,  or  alkalies,  are  substances  or 
compounds  such  as  household  ammonia  (NH4OH); 
potash  lye  (KOH),  which  is  also  called  caustic  potash; 
soda  lye,  or  caustic  soda  (NaOH);  and  slaked  lime 
(CaO2H2),  which  is  used  for  building  purposes. 

In  the  home  the  bases  are  more  commonly  used  than 
the  acids.  They  are  used  largely  for  cleansing  purposes, 
and  potash  lye  is  used  for  making  soap.  The  lye, 
properly  diluted,  is  very  valuable  for  removing  grease 
from  drain  pipes  and  sinks.  Household  ammonia  is 
ammonia  in  diluted  form,  and  a  small  amount  in  water 
is  very  useful  for  house  cleaning,  and  also  for  washing  deli- 
cate fabrics  and  for  the  removal  of  stains  and  grease  spots. 

The  strong  bases,  like  the  acids,  must  be  used  with 
considerable  care  and  caution.  If  they  come  in  contact 
with  the  hands  or  clothing,  they  have  a  caustic  or  "eating" 
effect  and  usually  will  discolor  the  clothing.  If  a  base  is 
spilled,  it  can  be  neutralized  by  pouring  on  it  at  once 
some  dilute  acid.  The  best  acids  to  use  for  this  purpose 
are  hydrochloric  and  acetic  acids.  In  the  home,  lemon 
juice  or  vinegar  would  do.  If  any  acid  is  spilled,  it  can 
be  neutralized  by  pouring  on  it  at  once  a  base.  Am- 
monia is  the  best,  as  it  is  the  least  harmful  if  too  much 
of  it  should  be  used.  The  strong  acids  and  bases  act 
very  quickly  on  the  body  and  clothing,  and  in  case  of 
accident  the  neutralizer  must  be  used  without  delay  or 
the  harmful  work  will  be  done  and  there  will  be  no  remedy. 
A  base  will  neutralize  an  acid  and  an  acid  will  neutralize 
a  base.  Limewater,  a  mild  base,  is  sometimes  prescribed 
by  physicians  to  neutralize  the  acids  in  the  stomach  and 
thus  aid  digestion. 


CHEMISTRY  OF   COMMON  THINGS 


Bases  in  dilute  form  have  a  bitter  taste  and  some 
(potash  lye  and  soda  lye)  have  a  soapy,  slimy  feeling. 
Bases  will  turn  red  litmus  paper  blue.  If  blue  litmus 
paper  is  dipped  in  acid  it  will  become  red.  This  red 
litmus  paper,  if  placed  in  a  base  solution,  will  turn  blue. 
Bases  will  turn  colorless  phenolphthalein1  red  and  acids 
will  make  the  red  disappear.  This  is  a  very  delicate  test 
for  a  base.  Acids  and  bases  react  on  each  other  in  such 
a  way  that  the  one  undoes  the  work  of  the  other. 

13.  Neutral  Substances.  —  Neutral  substances  are 
formed  by  the  interaction  of  a  base  and  an  acid.  For 
instance,  when  the  proper  proportions  of  hydrochloric 
acid  (HC1)  and  caustic  soda  (NaOH)  are  poured  together 
in  a  vessel,  two  new  substances  will  be  formed  and  both 
of  them  will  be  neutral.  The  two 
new  compounds  thus  formed  are 
water  (H2O)  and  common  table 
salt  (NaCl).  The  common  salt 
will  of  course  be  dissolved  in  the 
water,  but  can  be 
made  to  crystallize 
if  the  solution  is 
heated  so  that  the 
water  evaporates. 
The  way  to  make 
a  neutral  solution 
by  mixing  a  base 
and  an  acid  is  as 
follows:  Put  into 
a  test  tube  or  other  vessel  a  small  quantity  of 
an  acid  and  then  place  in  it  a  small  piece  of  litmus 
paper  and  note  the  color.  Now  slowly  pour  in  a  base 

1  See  Glossary. 


FORMING  A  NEUTRAL  SUBSTANCE 
By  mixing  a  base  and  an  acid. 


16  GENERAL  SCIENCE 

solution,  until  the  litmus  paper  turns  blue.  Take  a 
dropper,  made  out  of  a  small  glass  tube,  and  put  in 
acid  drop  by  drop  until  the  litmus  begins  to  turn 
red.  If  you  get  in  too  much  acid,  use  a  small  drop 
of  the  base.  When  the  solution  is  neutral  the  litmus 
paper  will  have  a  bluish-red  color.  When  you  think 
the  solution  is  neutral,  put  in  a  few  drops  of  phenol- 
phthalein,  which  will  remain  colorless  if  the  solution  is 
neutral  or  if  it  has  an  excess  of  acid.  If  there  is  the 
least  excess  of  base,  the  phenolphthalein  will  turn  red. 

From  our  study  of  acids  and  bases  we  learned  that 
they  will  corrode  or  rust  metals,  discolor  clothing,  and 
even  eat  a  hole  in  it.  But  none  of  these  three  things  will 
be  done  by  a  neutral  substance  or  a  substance  almost 
neutral.  The  three  unfavorable  effects  of  strong  bases 
will  show  us  why  they  cannot  be  used  generally  for 
washing  clothing  or  bathing.  So  a  milder  cleansing 
agent,  namely  soap,  which  will  remove  the  dirt  without 
injuring  the  clothing,  has  been  made. 

14.  How  Soap  is  Made. —  Fats  or  oils  taken  from 
plants  or  animals,  and  a  base  (soda  lye  or  potash  lye) 
are  used  in  soap  making.  Fats  are  salts  in  which 
glycerine  acts  as  the  base  and  stearic,  palmitic,  and 
oleic  acids  act  as  acids.  When  fats  are  heated  with 
caustic  potash  (KOH),  glycerine  is  formed  and  set  free, 
while  the  potassium  of  the  potash  unites  with  the  acids 
of  the  fat  and  forms  a  salt  called  soap.  The  oxygen  and 
hydrogen  of  the  caustic  potash  help  to  form  the  free 
glycerine.  The  soaps  made  with  caustic  potash  are  soft 
soaps.  When  fats  are  heated  with  caustic  soda  (NaOH), 
glycerine  is  formed  and  set  free,  while  the  sodium  unites 
with  the  acids  of  the  fat  and  forms  hard  soap.  Hard 
soap  can  also  be  made  by  using  potash  lye,  if  common 


CHEMISTRY  OF  COMMON  THINGS 


Sweat  Pore 


HAIR 


salt  is  added  when  the  soap  is  through  cooking.  While 
cooling  the  soap  will  rise  to  the  surface  and  leave  the 
brine,  alkali,  and  glycerine  in  the  solution.  Liquid  soap  is 
made  by  adding  water  to  the  soft  soap  until  it  flows  as 
freely  as  desired.  Liquid  soap  is  more  sanitary  than  hard 
soap,  especially  in  schools,  railroad  stations,  and  other 
public  buildings,  as 
it  prevents  more 
than  one  person 
from  handling  the 
same  soap. 

Cheap  laundry 
soaps  are  made  of 
resin  and  waste 
lard,  butter,  tallow, 
scraps  of  meat, 
waste  fat,  and  kit- 
chen refuse  and  an 
excess  of  a  strong 

base.    The    excess  °ffll'/l  U  W  "t» 

base  makes  them 
very  hard  on  the 
hands  and  also  on 
fine  fabrics.  Fine 
toilet  soaps  are  made  of  pure  plant  oils  and  enough  of 
the  base  to  make  them  almost  neutral  but  leave  them 
slightly  basic.  (Ask  your  teacher  or  parents  to  tell  you 
how  your  great-grandparents  used  to  prepare  potash  for 
soap  making.) 

15.  How  Soap  Cleans.  —  The  hands,  face,  and  other 
parts  of  the  body  are  kept  soft  by  an  oil  which  is  secreted 
by  the  glands  in  the  skin.  When  the  hands  and  face  are 
washed  several  times  without  soap,  as  when  out  camping, 


Cell 


VERTICAL  SECTION  OF  THE  SKIN 

Note  the  relative  size  of  the  oil  glands. 
(Magnified.) 


i8 


GENERAL   SCIENCE 


this  oil  is  not  removed  from  the  skin  and  so  the  water 
cannot  remove  the  dirt.  To  understand  how  the  soap 
removes  this  oil  it  will  be  necessary  to  know  what  an 
emulsion  is  and  how  it  is  made. 

When  little  particles  of  fat  are  broken  up  so  finely 
that  they  seem  to  mix  and  disappear  in  water,  this  mix- 
ture of  particles  of  fat  and  water  is  called  an.  emulsion. 
Milk  is  a  typical  ex- 
ample of  a  good  emul- 
sion in  which  the  fat 
globules    rise    to    the 
surface  as  cream,  if  it 
is    allowed    to    stand 
for  several  hours.    An 
emulsion  can  be  made 


GLOBULES  OF  FAT  IN  MILK 
A  good  type  of  an  emulsion.    (Magnified.) 

by  taking  some  oil  and 

shaking  it  with  some  base  in  a  test  tube.  The  base 
breaks  up  the  oil  into  fine  globules  so  that  they  mix 
with  the  solution  easily. 

Since  all  soaps  are  slightly  basic,  the  base  acts  on  the 
oil  or  grease  on  the  hands  and  face  and  forms  an  emulsion 
which  mixes  with  the  wash  water  and  then  the  water  easily 
takes  the  dirt  away  also.  The  same  is  true  of  the  re- 
moval of  dirt  from  clothing,  except  that  usually  a  soap 
is  used  having  a  greater  excess  of  base,  which  forms  an 
emulsion  of  the  grease  in  the  clothing  and  sets  the  dirt 
free. 

Nearly  everyone  is  familiar  with  the  fact  that  soap 
does  not  work  well  in  all  kinds  of  water.  In  some  water 
soap  will  easily  form  an  emulsion  of  fat  and  also  a  good 
lather  or  soap  foam.  This  water  is  said  to  be  "soft" 
water,  and  it  does  not  contain  any  chemical  that  will 
act  on  soap  and  prevent  the  formation  of  an  emulsion. 


CHEMISTRY  OF  COMMON  THINGS  19 

The  other  kind  of  water  contains  chemical  compounds 
which  will  act  on  soap  and  prevent  the  formation  of  an 
emulsion.  This  water  is  said  to  be  "hard"  water,  and 
a  lather  will  not  form  in  hard  water  or  in  water  contain- 
ing chemicals  that  act  on  soap. 

16.  Hard  Water.  —  Water  flowing  over  the  ground 
and  through  the  ground  comes  in  contact  with  more  or 
less  salts  that  can  be  dissolved  and  carried  along  in 
solution.  If  these  salts  held  in  solution  happen  to  be 
what  are  known  as  the  calcium  salts,  as  calcium  hydrogen 
carbonate  [CaH2(COj)i],  or  calcium  sulphate  (CaSO4), 
which  is  also  known  as  gypsum,  the  water  will  be  "hard" 
water.  When  soap  is  used  in  hard  water  a  sticky, 
gummy-like  substance  is  formed  which  will  not  dissolve 
in  the  water  and  which  is  known  as  calcium  soap.  Cal- 
cium soap  is  not  fit  for  washing  as  it  will  not  form  an 
emulsion  with  fats.  In  hard  water  the  soap  is  wasted 
until  the  calcium  compounds  are  all  broken  up  by  the 
soap.  This  is  an  expensive  way  of 
making  the  water  "soft,"  so  cheaper 
chemicals  are  used  to  soften  water. 

Water  containing  calcium  hydro- 
gen carbonate  [CaHj(COj)sJ  is  said 
to  be  "temporarily  hard"  because  it 
can  be  softened  by  adding  a  measured  TEAKETTLE 

quantity  of  slaked  lime  (CaO2H2),  or 
by  boiling  it  for  a  time.  The  slaked 
lime  acting  on  the  calcium  hydrogen  carbonate  forms 
a  white  precipitate,  calcium  carbonate  (CaC03),  which 
will  settle,  and  then  you  may  draw  off  the  clear,  soft 
water.  The  stone-like  scale  in  a  teakettle  in  which  hard 
water  is  continually  heated  is  due  to  the  settling  of  the 
insoluble  compound,  calcium  carbonate,  (CaCO3)  formed 


20  GENERAL  SCIENCE 

by  the  action  of  the  heat  on  the  calcium  hydrogen 
carbonate. 

Water  containing  calcium  sulphate,  or  gypsum  (CaS04), 
is  said  to  be  "  permanently  hard/'  because  it  can  be 
softened  only  by  removing  the  water  from  the  gypsum 
by  distillation  or  by  adding  some  substance  such  as 
borax,  ammonium  carbonate,  or  washing  soda  (Na2CO3), 
also  called  sodium  carbonate.  These  substances  are 
cheaper  than  soap  and  they  break  up  the  gypsum  and 
form  substances  which  will  not  act  on  soap.  But  these  new 
substances  are  hard  on  the  clothes  and  also  on  the  hands 
of  the  laundry  workers,  so  it  is  better  to  use  "soft"  water. 

17.  Salts.  —  A  number  of  compounds  which  can  be 
classed  as  salts  have  already  been  mentioned.  Salts  are 
formed  by  the  interaction  of  a  base  and  an  acid.  If,  as 
described  in  §13,  just  enough  base  is  used  to  neutralize 
the  acid,  a  neutral  salt  is  formed.  Common  salt  and 
sal  ammoniac  and  gypsum  are  examples  of  neutral  salts. 
If  an  excess  of  a  base  is  used  with  an  acid,  a  basic  salt 
is  usually  formed.  If  an  excess  of  an  acid  is  used,  an 
acidic  salt  is  usually  formed.  Cream  of  tartar  is  an 
example  of  an  acidic  salt. 

There  are  great  quantities  of  common  salt  and  other 
salts  stored  in  the  earth,  which  have  been  there  for  long 
ages.  Salt  is  taken  from  the  earth  in  various  parts  of 
the  United  States  by  drilling  wells  and  pumping  out  the 
salt  water,  by  digging  mines,  and  in  California  it  can  be 
shoveled  from  the  surface.  The  salt  water  or  brine  is 
allowed  to  evaporate  and  then  the  salt  will  form  in  -crys- 
tals. The  largest  salt  mines  are  in  Germany,  where  the 
salt  is  about  a  mile  deep.  This  salt  was  perhaps  deposited 
during  the  evaporation  of  an  ancient  inland  sea,  such  as 
the  Caspian,  or  the  Great  Salt  Lake  in  Utah. 


CHEMISTRY  OF  COMMON  THINGS 


21 


Great  quantities  of  common  salt  are  used  in  cooking 
and  preserving  meats  and  other  foods,  but  much  more 
is  used  in  the  manufacture  of  washing  soda,  soap,  glass, 
bleaching  powders,  baking  powders,  baking  soda,  etc. 
About  4,000,000  tons  are  used  annually  in  the  United 
States  alone. 


MAKING  SALT  BY  EVAPORATION  IN  CALIFORNIA 


QUESTIONS  AND   EXERCISES 

1.  Your  mother  hangs  wet  clothing  on  the  line  to  dry.    Where 
does  the  water  go?     What  becomes  of  sweat  on  your  body? 

2.  Test  with  litmus  paper  the  compounds  which  you  have  at 
home.     (Dry   substances   must   be   dissolved   in   water.    Test   the 
water  before  using  to  see  if  it  affects  the  litmus.)     Make  a  list  of 
them  as  follows: 


Name  of  compound  .  .  .Acid  Base  Neutral  salt 
Baking  soda  (       )?  (     )?  ( 
Vinegar  (       }?  (     }?  ( 

Soaps 

f     )?         (    )?              r 

Etc. 

1  Neutral  salts  do  not  affect  red  or  blue  litmus. 


22  GENERAL   SCIENCE 

3.  Make  some  soap  by  boiling  a  mixture  of  lard  and  some  strong 
base,  as  potash.     (To  see  if  the  soap  is  done,  mix  a  little  of  it  with 
soft  water.     If  no  fat  globules  appear  on  the  surface  of  the  water 
the  soap  is  ready  for  use.) 

4.  Make  an  emulsion  by  thoroughly  mixing  a  fat  or  oil  with  some 
base  and  water.     Let  it  stand  a  few  hours  to  see  if  the  fat  will  come 
to  the  surface. 

5.  If  you  have  no  hard  water,  make  some  by  adding  a  few  drops 
of  some  acid  or  calcium  sulphate  solution,  and  divide  the  water  into 
two  parts.    Try  some  soap  in  one  part  and  observe  the  result.    Place 
some  washing  soda  in  the  other  part  and  then  try  soap  in  it.     Now 
compare  the  result  with  that  of  the  first  trial. 

6.  Examine  the  inside  of  your  teakettle  to  see  if  any  hard  sub- 
stance has  collected  on  the  bottom  and  sides.     If  so,  what  is  it? 


CHAPTER  IV 
CHEMISTRY    OF   BAKING 

18.  Cooking  improves  the  flavor  and  makes  more 
digestible  most  articles  of  food.  There  are  two  ways  of 
preparing  food  from  plant  sources.  One  is  to  heat  it  in 
water  or  other  liquid,  which  softens  the  connective  tissue 
so  that  it  is  easily  broken  up  and  the  cells  set  free  for  the 
action  of  the  digestive  fluids  of  the  body.  The  other 
way  is  to  subject  the  food  to 
dry  heat,  as  in  an  oven,  where 
a  much  higher  temperature 
than  that  of  boiling  water  can 
be  obtained.  Plant  foods  pre- 
pared in  the  oven  have  some 
water  or  moisture  in  them,  as 
liquids  are  used  in  mixing  the 
various  kinds  of  flours.  Even 
popcorn,  though  very  dry, 
bursts  open  when  heated,  be- 
cause  the  moisture  in  it  turns 
into  steam. 

The  heat  causes  the  starch  grains  of  vegetables  and 
grains  to  enlarge  and  burst  the  connective  tissue  holding 
them,  and  also  changes  a  little  of  the  starch  into  a  form 
of  sugar  called  dextrin,  and  the  part  remaining  is  then 
easily  changed  to  sugar  by  the  digestive  fluids.  Striking 
examples  of  this  change  of  starch  to  dextrin  sugar  are 
the  differences  in  taste  between  a  raw  and  a  cooked 


STARCH  GRAINS 
In    cells    of  potato    as    they 


GENERAL  SCIENCE 


potato,  and  raw  flour  and  bread  well  baked.  This 
dextrin  sugar,  formed  in  the  bread  while  baking,  is  turned 
into  caramel  on  the  surface  of  the  loaf,  where  the  tempera- 
ture is  very  high,  and  gives  to  the  bread  crust  the  brown 
color.  Caramel  is  also  formed  when  bread  is  toasted. 

Bread  made  from  corn  meal  is  not  porous  or  full  of 
small  holes  like  bread  made  from  wheat  flour.  Wheat 
flour  has  in  it  a  form  of  albumin  called  gluten.  This 

gluten  when  moistened  is  very 
tough  and  gummy  and  does 
not  permit  the  gases  formed  in 
the  dough  to  escape.  The  gas 
formed  in  the  dough  raises  it. 
When  the  dough  is  placed  in 
the  oven,  the  gas  in  it  expands 
because  of  the  intense  heat  and 
so  raises  the  dough  still  more, 
so  that  the  heat  can  affect  the  starch  and  albumin  in  all 
parts  of  the  loaf, —  that  is,  bake  it  clear  through.  There 
are  several  ways  of  forming  this  gas  in  the  dough;  these 
may  be  classed  as  follows:  i.  By  the  use  of  chemicals. 
2.  By  the  use  of  a  one-celled  plant  (yeast).  3.  By  a  me- 
chanical method  such  as  is  sometimes  used  in  baking 
cakes,  viz.  beating  the  dough  violently  to  get  air  mixed 
with  it,  which  will  expand  when  the  dough  is  placed  in 
the  oven,  and  thus  raise  it. 

19.  Baking  Soda  (NaHC03).  —  Baking  soda  is  also 
known  as  bicarbonate  of  soda  and  sodium  hydrogen  car- 
bonate. It  is  a  salt,  slightly  basic  in  its  reactions  on  other 
compounds.  When  it  is  acted  on  by  an  acid,  such  as 
sour  milk,  carbon  dioxide  is  set  free.  If  it  is  mixed  with 
the  dough  without  the  use  of  a  mild  acid,  the  carbon 
dioxide  will  be  liberated  by  the  action  of  the  heat  while 


'Gluten  Cells 

A  GRAIN  OF  WHEAT 

Showing  starch  and  gluten. 
(Magnified.) 


CHEMISTRY  OF  BAKING  25 

baking.  The  carbon  dioxide  is  what  raises  the  dough 
when  baking  soda  is  used.  If  the  soda  is  not  completely 
dissolved  and  mixed  with  the  dough,  yellow  spots  will 
appear  in  the  bread  or  biscuits.  One  sure  way  of  pre- 
venting this  is  to  dissolve  the  soda  in  water  and  then 
mix  it  with  the  flour  or  dough.  A  less  sure  way  of  pre- 
venting the  yellow  spots  is  to  sift  the  soda  with  the  flour. 

When  baking  soda  in  solution  or  in  the  dough  is  heated, 
carbon  dioxide  is  liberated,  and  another  salt  called  wash- 
ing soda  (Na2CO3)  is  formed.  This  stays  in  the  bread 
and  is  not  healthful. 

20.  Baking  Powder.  —  Baking  powder  is  a  mixture  of 
two  salts  and  some  corn  starch  to  keep  it  dry.  Baking 
powder  does  not  form  washing  soda  in  the  bread  and  so 
is  better  for  baking  than  soda.  The  object  in  using  any 
such  compound  in  baking  is  to  liberate  carbon  dioxide 
to  raise  the  dough.  Carbon  dioxide  will  be  liberated  if 
baking  soda  is  used  with  an  acid.  Hence,  in  making 
baking  powder,  baking  soda  is  mixed  with  a  mild  acid 
salt  which  will  not  form  a  harmful  salt  in  the  bread. 
(Caution.  —  Sometimes  in  making  baking  powder  a 
cheap  acid  is  used  that  will  form  a  harmful  substance 
in  the  cake  or  bread.  These  are  called  the  alum  baking 
powders  and  they  should  not  be  used.) 

The  good  baking  powders  are  made  of  two  parts  of 
cream  of  tartar  (KHC4H4Oe),  one  part  of  baking  soda,  and 
some  corn  starch.  Tartaric  acid  (HC4H4O6)  and  calcium 
acid  phosphate  [CaH4(PO4)2]  may  also  be  used  with 
baking  soda  to  make  the  baking  powder.  The  sub- 
stances formed  in  the  bread  by  these  powders  are 
perfectly  harmless. 

In  making  baking  powders  baking  soda  is  mixed  with 
the  acidic  salts,  but  no  chemical  action  will  take  place 


26 


GENERAL  SCIENCE 


while  they  are  dry.  If  water  is  mixed  with  the  powders, 
a  reaction  will  occur  during  which  all  the  carbon  dioxide 
will  escape.  For  this  reason  baking  powder  should 
be  thoroughly  mixed  with  the  dry  flour  before  making 
the  dough,  then  the  carbon  dioxide  will  not  be  formed  so 
rapidly  and  will  not  escape.  Self-rising  flour  has  baking 
powder  mixed  with  it. 

How  to  test  baking  powders  for  alum.  —  Burn  two  or 
three  grams  of  the  powder  in  a  porcelain  dish.  Mix  the 

ash  left  in  the 
dish  with  boiling 
water  and  filter. 
Add  to  the  fil- 
trate (the  filtered 
solution)  enough 
ammonium  chlo- 
ride solution  so 
the  mixture  will 
have  a  distinct 
odor  of  ammonia. 

Look  for  white  flakes  in  the  solution.  If  none  appear 
immediately,  warm  the  solution  slowly.  These  white 
flakes,  if  any,  are  composed  of  an  alum  compound  and 
indicate  the  presence  of  alum  in  the  baking  powder. 

21.  Baking  soda  and  baking  powders  are  used  only 
when  not  much  time  is  taken  and  in  baking  in  small 
quantities  such  foods  as  cakes,  pies,  biscuits,  and  corn 
bread.  They  are  used  in  making  corn  bread  because 
corn  meal  does  not  have  any  albumin  in  the  form  called 
gluten  to  hold  the  carbon  dioxide  set  free  by  the  slow 
action  of  yeast.  The  corn  bread  must  be  baked  as  soon 
as  the  mixture  is  made. 

There  are  several  reasons  why  baking  powder  is  not 


FUNNELS  FOR  FILTERING 
Three  ways  of  supporting  them. 


CHEMISTRY  OF  BAKING 


27 


used  in  making  "light"  bread.  It  would  require  such  a 
large  quantity  of  it  to  raise  the  dough  that  it  would  be 
much  more  expensive  than  yeast.  The  taste  of  biscuits 
baked  in  a  few  minutes  after  mixing  the  dough  is  quite 
different  from  the  taste  of  bread  which  has  been  given 
several  hours  for  the  dough  to  rise.  This  difference 
in  the  taste  of  " light"  bread  and  biscuits  is  due  to 
three  things,  i.  Growth  of  the  yeast  plant  takes  place 
in  the  dough.  2.  The  wheat  grain  has  a  ferment  in  it 

called   diastase.     This  dia-    , ; . 

stase  is  in  the  flour  made 
from  wheat,  and  it  changes 
some  of  the  starch  in  the 
flour  to  sugar  while  the 
bread  is  rising.  It  takes 
several  hours  for  the  dia- 
stase to  change  much  of 
the  starch  to  sugar,  and 
so  it  does  not  have  time 
to  act  in  the  quickly  made 
biscuits.  3.  Heat  changes 
starch  to  dextrin  sugar,  but 
it  must  have  time  to  do  so.  The  heat  has  a  longer  time 
to  act  on  the  large  loaf  than  it  does  on  the  small  biscuit. 
22.  Yeast.  —  Yeast  is  a  plant  so  small  that  a  good 
microscope  is  necessary  to  see  it.  It  consists  of  only 
one  cell.  The  plant  grows  by  each  cell  dividing  into  two 
unequal  parts.  The  smaller  part  is  called  a  bud  while 
attached  to  the  larger  part.  When  a  yeast  plant  does 
not  have  food  enough,  it  grows  a  tough  protective  cover- 
ing over  itself,  and  then  can  dry  sufficiently  to  be  carried 
by  the  wind  with  the  dust  and  float  about  in  the  air. 
On  this  account  the  air  is  full  of  yeast  plants,  but  they  are 


YEAST  PLANTS 
(Magnified.) 


28  GENERAL  SCIENCE 

so  small  that  they  cannot  be  seen.  These  floating  yeast 
plants  are  called  wild  yeast.  When  they  fall  into  liquids 
containing  small  quantities  of  sugar  they  start  to  grow 
and  soon  spoil  the  liquids.  While  yeast  is  in  the  air  or 
on  dry  material,  it  remains  inactive,  just  as  do  seeds  that 
are  not  planted.  When  it  falls  in  places  favorable  for 
growth,  it  throws  off  its  protective  covering  and  absorbs 
the  food.  The  conditions  favorable  for  its  growth  are: 
i.  Temperature  from  70°  to  100°  F.  (Bread  rises  best 
in  a  temperature  of  from  80°  to  95°  F.)  2.  Moisture  in 
sufficient  quantity  to  dissolve  the  food.  3.  Food  in 
solution.  When  these  three  conditions  are  present  a 
few  yeast  plants  will  soon  increase  to  thousands.  While 
they  are  growing,  they  give  off  two  waste  products. 
The  important  one  in  bread-making  is  carbon  dioxide 
gas.  This  gas  causes  the  dough  to  expand  and  become 
spongy,  thus  making  the  bread  light  and  porous  after 
baking.  The  only  reason  why  yeast  is  used  in  baking 
is  because  of  this  carbon  dioxide  gas  which  it  forms  in 

the  dough.  It  also  gives 
off  alcohol  as  a  waste 
product.  But  so  little 
of  this  is  formed  in  the 
dough  while  rising  that 

it  is  all  driven  out  by 
ANCIENT  GRINDING  STONES  ,.          ,      .         ,, 

evaporation   during   the 

process  of  baking.  Alcohol  boils  at  a  lower  temperature 
than  water  and  so  will  evaporate  faster  and  more  easily. 
23.  History  of  Bread  Making.  —  The  ancients  made 
bread  in  a  way  somewhat  similar  to  the  method  of  the 
savage  tribes  of  today.  They  crushed  the  grain  with  a 
hand  tool  of  wood  or  stone  and  made  a  paste  of  the  meal 
with  water  and  then  baked  it  by  holding  it  over  a  fire. 


CHEMISTRY  OF  BAKING  29 

The  result  was  a  hard,  compact  mass  called  unleavened 
bread,  which  was  very  hard  to  masticate,  and  the  taste 
was  not  that  of  modern  bread.  If  the  paste  made  of 
water  and  crushed  grain  was  allowed  to  stand  for  a  few 
hours,  the  wild  yeast  of  the  air  would  fall  into  it  and  start 
to  grow  and  produce  carbon  dioxide  gas.  This  made 
a  more  porous  loaf  than  the  unleavened  bread  and  was  a 
great  improvement  over  it.  It  was  called  self -raised  bread. 

This  was  discovered  perhaps  by  some  good  housewife 
who,  after  making  her  batter,  had  to  attend  to  some  other 
duties  for  a  few  hours  and  on  returning  found  that  her 
dough  had  increased  in  size.  This  she  baked  and  found 
that  it  had  a  better  quality  than  any  she  had  ever  tasted, 
so  after  this  she  let  all  of  her  dough  stand  a  few  hours 
before  baking,  and  of  course  told  her  neighbors  about 
her  new  bread. 

Soon  it  was  also  learned  that  if  a  bit  of  this  self- 
raised  dough  was  saved  and  put  into  the  next  baking, 
the  batter  would  rise  much  faster  and  be  much  more 
porous  and  eatable  than  the  self-raised  bread.  This 
was  another  great  improvement  and  was  widely  used  for 
many  centuries.  It  is  used  somewhat  even  today.  A 
very  similar  method  was  used  by  the  Romans.  They 
learned  that  grape  juice  mixed  with  millet  would  grow 
yeast  plants  rapidly,  so  they  used  this  mixture  for  bread 
raising  by  kneading  a  small  quantity  of  it  into  the  dough, 
then  allowing  the  dough  to  stand  a  while  before  baking. 

Through  all  these  centuries  the  results  of  fermentation 
were  known  and  used,  but  it  was  not  known  that  the 
yeast  plant  was  the  cause,  nor  until  the  nineteenth  cen- 
tury did  anyone  know  that  there  was  such  an  organism 
as  the  yeast  plant.  The  microscope  was  necessary  to 
discover  the  little  plant  in  fermenting  liquids,  to  learn 


3d  GENERAL  SCIENCE 

how  it  grew,  and  that  it  could  change  sugar  into  alcohol 
and  carbon  dioxide.  Alcohol  was  known  ages  ago, 
but  it  was  not  known  that  alcohol  is  a  poisonous  -waste- 
product  of  the  yeast  plant. 

The  yeast  was  studied  until  a  way  was  found  by  which 
it  could  be  grown  in  great  amounts  for  bread  making  and 
for  the  production  of  alcohol  and  the  various  intoxicating 
drinks  containing  alcohol.  The  commercial  yeast  in 
the  form  01  cakes  consists  of  a  great  number  of  yeast 
plants  without  sufficient  moisture  and  food  for  growth. 
When  this  commercial  yeast  is  mixed  with  dough,  the 
yeast  plants  begin  to  grow  and  increase  rapidly,  giving 
off  carbon  dioxide  which  raises  the  batter,  and  when 
this  is  baked  it  is  our  modern  bread. 

QUESTIONS  AND  EXERCISES 

1.  Taste  the  brown  crust   of  well-baked  bread,   and  then  the 
white  inner  part.     Make  note  of  any  difference. 

2.  Examine  the  texture  of  wheat  bread  and  that  of  corn  bread. 
Explain  the  difference  and  its  causes. 

3.  Dissolve  some  baking  soda  in  water  and  observe  the  result. 
Now  add  a  few  drops  of  vinegar.     Explain  what  happens.     What 
made  the  bubbles? 

4.  Dissolve   some   baking   powder   in   water.     Does   it   act   the 
same  as  baking  soda?    Why? 

5.  From  what  you  have  observed,  how  should  baking  soda  and 
baking  powder  be  put  into  the  baking  material? 

6.  Why  do  good  soda  biscuits  taste  different  from  raised  bread? 

7.  Dissolve  a  teaspoonful  of  sugar  in  a  gill  of  water  and  mix  with 
it  a  small  quantity  of  yeast.     Place  it  for  a  few  hours  where  the 
temperature  is  70°  to  95°  F.     Note  and  explain  the  gas  bubbles. 

8.  If  you  have  a  microscope,  place  one  drop  of  the  solution  on  a 
glass  slide  and  examine. 


CHAPTER  V 
PRESERVATIVES   AND    DISINFECTANTS 

24.  Germs.  —  The  world  is  full  of  many  kinds  of 
microscopic  living  organisms.  They  are  one-celled  bodies. 
Some  are  animals  and  some  are  plants.  The  one-celled 

plants  are  known  as  bacteria. 
Most  of  the  bacteria  are  very 
valuable  and  serviceable  to 

man.     Some    of    these    are  in 
BACTERIA  OF  VARIOUS  KINDS       ,  . 

the  soil  and  prepare  food  for 

Magnified  1000  diameters. 

the   trees   and   vegetables   and 

grains  upon  which  man  is  dependent  for  food.  Others 
are  useful  in  souring  milk,  ripening  cheese,  and  making 
cider  vinegar.  Others  decompose  dead  matter,  such  as 
fallen  trees,  grass,  and  dead  animals,  and  thus  prevent 
them  from  collecting  in  quantity  on  the  earth. 

But  when  these  act  on  things  which  man  wants  to 
keep,  then  they  are  considered  harmful.  They  will 
decompose  railroad  ties, 
telephone  poles,  all  kinds 
of  wood  fixtures,  meats, 
and  other  foods.  Mold  is 
also  very  destructive.  It 
will  destroy  bread,  damp 
clothing,  fruits,  etc.  The 
yeast  plant  is  also  respon- 
sible for  the  souring  of 


MOLD  PLANTS 
(Magnified.) 


GENERAL  SCIENCE 


fruit  juices.  In  order  to  protect  his  property,  man  had 
to  find  ways  of  preventing  the  growth  of  these  tiny 
plants  called  yeast,  mold,  and  bacteria.  A  few  bacteria 
and  one-celled  animals  live  as  parasites  in  man  when 
they  get  a  chance,  and  are  called  disease  germs.  Each 
kind  causes  a  different  disease. 


TYPES  OF  GERMS 

From  left  to  right,  top  row:   Pus,  Tuberculosis,  Tetanus;   bottom  row: 
Pneumonia,  Diphtheria,  Typhoid. 

Many  physicians  are  spending  their  lives  in  studying 
disease  germs,  and  some  wonderful  results  have  been 
accomplished.  These  physicians  tell  us  that  it  is  much 
easier  to  prevent  disease  than  it  is  to  cure  it.  When 
the  germs  get  into  our  bodies,  they  are  very  hard  to  kill 
without  injuring  the  body.  Some  germs  the  physicians 
are  not  yet  able  to  kill  while  they  are  in  the  human  body, 
and  the  diseases  caused  by  such  germs  are  said  to  be 
incurable.  What  are  some  incurable  diseases? 

The  air  contains  many  of  these  dangerous  germs  be- 


PRESERVATIVES  AND   DISINFECTANTS 


33 


cause  of  the  carelessness  and  ignorance  of  so  many  people. 
They  get  into  the  water  we  drink  and  the  food  we  eat. 
Our  bodies  are  able  to  kill  these  germs  by  thousands  if 
we  keep  healthy  by  regular  habits  of  exercise  and  sleep, 


PASTEURIZING  AND  BOTTLING  APPARATUS  FOR  MILK 
The  milk  is  kept  at  140°  F.  for  thirty  minutes.     About  98  per  cent 
of  the  bacteria  are  killed.     (From  La  Flam  Creamery.) 

and  take  nothing  into  our  bodies  but  pure  food  and  pure 
water. 

25.  How  to  Destroy  the  Germs.  —  Since  the  germs 
are  very  numerous  and  so  many  people  are  not  healthy 
and  so  many  are  careless,  it  will  be  well  to  know  how  to 


34  GENERAL  SCIENCE 

keep  them  out  of  our  bodies.  They  are  much  more  easily 
killed  if  where  we  can  get  at  them  than  when  they 
are  in  the  body.  Since  many  of  the  germs  live  best  in 
dark,  moist  places,  sunshine  is  the  best  natural  germ 
destroyer  or  disinfectant  that  man  can  use.  Let  the 
sunshine  into  the  rooms  of  all  buildings.  The  faded 
paper  on  the  wall  will  not  cost  as  much  as  sickness 
and  moderately  poor  health.  Hang  clothing,  carpets, 
and  bedclothes  in  the  sunshine  and  air.  The  wind  and 
sunshine  work  together  killing  germs. 

(A)  Germs  and  Heat.  —  Germs  cannot  stand  a  very 
high  temperature.  Boiling  water  will  kill  most  germs  in 
a  short  time.  For  this  reason  the  bedding  and  clothing  of 
a  person  who  has  a  germ  disease  such  as  diphtheria, 
typhoid  fever,  measles,  tuberculosis,  etc.  should  be 
washed  in  boiling  water  and  hung  to  dry  in  the  wind  and 
sunlight.  The  germs  in  milk  can  be  killed  by  boiling  it  or 
by  pasteurizing  it.  To  pasteurize  milk,  heat  it  to  from 
140°  to  150°  F.  for  about  thirty  minutes,  then  place  it 
in  closed  vessels  to  prevent  other  germs  from  entering. 
Many  of  the  diseases  of  children  can  be  avoided  by  using 
pasteurized  milk. 

Dishes  used  by  diseased  persons  can  be  made  harmless 
by  leaving  them  in  almost  boiling  water  for  a  few  minutes. 
Foods  that  are  well  cooked  or  baked  are  thoroughly  steri- 
lized. But  germs  may  get  into  such  foods  after  they  are 
cold,  by  being  handled  and  hauled  through  the  streets  for 
delivery,  as  is  done  with  bread  and  other  baked  articles. 
The  receptacles  for  canned  goods  should  be  placed  in 
the  sunshine  for  several  days  and  washed  in  boiling 
water  just  before  using.  Boiling  the  food  for  canning 
usually  kills  all  bacteria,  yeast,  and  mold  that  may  be 
.in  it.  If  it  is  placed  in  the  jars  while  hot  and  then 


PRESERVATIVES  AND  DISINFECTANTS  3$ 

sealed,  no  destructive  organisms  can  get  into  it,  and  it 
will  keep  for  a  year  or  more.  Mold  grows  little  seeds 
called  spores,  and  yeast  and  bacteria  can  form  a  protective 
covering  over  the  tiny  body  cell.  It  may  take  an  hour 
or  more  of  boiling  to  kill  these,  and  if  any  of  them  are  on 
the  food  to  be  canned  they  will  not  be  killed  by  the  few 


INSIDE  OF  PASTEURIZING  APPARATUS  FOR  MILK 

The  milk  is  heated  by  running  steam  through  the  coil.     After  thirty 
minutes  the  milk  is  cooled  by  causing  ice  water  to  flow  through  the  coil. 

minutes  of  boiling.  They  will  start  to  grow  in  the 
sealed  can  or  jar  and  cause  the  food  to  spoil  and  sometimes 
burst  the  can  open. 

When  wounds  or  sores  are  full  of  dangerous  disease 
germs,  physicians  kill  them  by  applying  a  very  hot 
piece  of  metal — ^a  tool  made  for  the  purpose.  A  strong 


36        ,  GENERAL  SCIENCE 

caustic  may  also  be  used.  This  method  of  sterilizing 
is  called  cauterization.  The  hot  iron  is  the  cauter. 

(B)  Germs  and  Chemicals.  —  Besides  sunshine,  heat, 
and  air,  man  has  learned  to  use  a  great  number  of  chemical 
compounds  to  fight  his  tiny  enemies,  the  germs,  which 
are  always  ready  to  attack  him  at  every  opportunity. 
More  persons  are  killed  in  the  fight  with  germs  than  in 
all  other  wars,  even  if  man  does  employ  many  weapons. 
Some  of  the  common  disinfectants,  or  substances  which 
will  kill  germs,  are:  lime  (unslaked),  chloride  of  lime, 
carbolic  acid,  sulphur,  formalin  or  formaldehyde,  mercuric 
chloride  or  corrosive  sublimate.  Most  of  these  are  rank 
poisons  and  must  be  used  with  care  and  caution. 

Air-slaked  lime  is  of  no  value  as  a  disinfectant,  for  it 
will  not  kill  germs.  Lime  slaked  in  water  forms  the 
caustic  lime  which  will  destroy  decaying  matter  as  well 
as  bacteria.  It  can  be  used  as  a  whitewash  for  barns, 
animal  pens,  and  outhouses,  and  when  put  on  by  a  spray 
pump  will  find  the  germs  in  all  the  cracks  and  corners. 
As  it  is  very  cheap  it  can  be  used  to  disinfect  wet  places 
and  outhouses  by  scattering  it  about  on  the  ground. 
Carbolic  acid  can  easily  be  mixed  with  the  whitewash, 
making  it  destructive  to  lice  and  other  insects. 

Chloride  of  lime  is  a  comparatively  cheap  disinfectant 
because  a  small  quantity  can  be  made  effective  over  a 
very  large  area.  A  few  pounds  in  a  large  street-sprinkling 
tank  will  kill  all  the  germs  in  the  dust  touched  by  the 
water  while  sprinkling.  It  is  also  very  effective  in 
garbage  cans  and  water-closets.  It  has  a  strong  odor  of 
chlorine,  for  chlorine  gas  is  liberated  when  the  chloride  of 
lime,  or  bleaching  powder,  is  acted  on  by  mild  acids  or 
when  it  is  exposed  to  the  air.  It  destroys  disease  germs 
by  indirect  oxidation. 


PRESERVATIVES  AND  DISINFECTANTS  37 

Carbolic  acid  is  a  strong  poison  and  must  be  used  with 
care.  It  can  be  mixed  with  water  for  washing  out  cup- 
boards and  mopping  floors  during  house-cleaning.  Three 
or  four  drops  in  a  teaspoonful  of  water  may  be  used  for 
washing  lingering  sores  on  animals  or  man.  When  mixed 
with  vaseline  it  is  good  for  killing  germs  in  sores. 

Sulphur  is  easy  to  use,  but  not  very  effective.  It 
will  not  kill  bacteria  in  the  spore  form,  that  is,  in  the 
form  in  which  they  are  dry  like  dust  and  lie  in  the 
cracks  and  corners  or  float  about  in  the  air.  The  sulphur 
dioxide  formed  by  burning  sulphur  requires  the  presence 
of  moisture  to  kill  germs.  To  fumigate  a  room  or  build- 
ing with  sulphur,  close  all  openings  as  tightly  as  possible. 
Place  in  the  middle  of  the  room  a  large  vessel  with  a  few 
inches  of  water  in  the  bottom,  and  in  the  center  place  a 
couple  of  bricks  on  edge  so  that  they  extend  out  of  the 
water.  Put  a  pound  or  two  of  powdered  sulphur  in  an 
iron  vessel  and  set  it  on  these  bricks.  Place  a  piece  of 
paper  soaked  in  alcohol  or  oil  down  into  the  sulphur, 
allowing  the  end  to  extend  out  above  the  sulphur.  Now 
open  all  the  closets  and  drawers  in  the  room  and  light  the 
paper,  leave  the  room,  and  close  the  door.  After  several 
hours  the  room  can  be  opened  and  aired.  Do  not  use 
the  room  until  the  sulphur  smell  is  gone. 

Formaldehyde  is  a  very  dangerous  poison,  but  is  one 
of  the  most  powerful  disinfectants.  It  is  used  by  bar- 
bers, dentists,  and  physicians  for  disinfecting  tools  and 
instruments.  The  tools  may  be  dipped  into  a  weak 
solution  or  laid  in  a  closed  case  filled  with  formalin  gas 
or  vapor.  It  may  be  used  in  water-closets  and  sick-rooms. 
Formaldehyde  candles  are  used  to  fumigate  sick-rooms 
in  much  the  same  way  as  sulphur. 

For  personal  disinfection  soap  and  water  will  remove 


38  GENERAL   SCIENCE 

the  dirt  and  germs  but  will  not  kill  them.  One  should 
always  wash  before  eating.  Before  performing  an  'opera- 
tion, physicians  wash  their  hands  and  dip  their  instru- 
ments into  hot  water  or  a  solution  of  formalin  and  then 
into  boiling  water.  Since  hydrogen  peroxide  liberates 
oxygen  readily,  it  makes  a  good  personal  disinfectant. 

(C)  Chemicals  as  Preservatives.  —  In  the  section  on 
Germs  and  Heat  we  learned  that  food,  sealed  up  air- 
tight after  the  bacteria,  mold,  and  yeast  had  been 
killed  by  boiling,  would  keep  for  a  long  time,  the  principle 
being  to  keep  these  tiny  plants  out  of  the  food  after  those 
in  it  have  been  killed.  In  the  section  on  Germs  and 
Chemicals  we  learned  that  these  germs  could  be  killed 
by  certain  compounds  as  well  as  by  the  use  of  heat  and 
sunshine. 

These  chemical  compounds  that  will  kill  germs  used  to 
be  employed  very  extensively  in  dilute  form  in  foods. 
When  the  bacteria  fell  into  these  foods  they  died,  and 
hence  the  food  would  not  decay  or  sour.  This  was 
cheaper  than  canning.  But  it  was  a  serious  menace  to 
health,  and  no  one  could  long  endure  the  constant 
use  of  such  poisonous  preservatives.  So  national  laws 
have  been  enacted  prohibiting  such  a  practice  and  re- 
quiring the  manufacturers  to  indicate  on  the  labels  the 
quantity  and  kind  of  chemicals  used,  if  any.  These 
laws  do  not  prevent  all  the  wrong  use  of  chemical  pre- 
servatives. There  are  always  some  people  who  will 
violate  law,  so  each  person  should  be  more  or  less 
on  his  own  guard  by  learning  the  facts. 

Borax  and  boric  acid  are  used  on  meats  and  will  restore 
tainted  meats  to  the  appearance  of  freshness.  Tainted 
meats  are  often  made  into  sausage  which  is  treated  with 
chemicals.  Benzoate  of  soda  is  used  in  catchup.  Cheap 


•PRESERVATIVES  AND  DISINFECTANTS  39 

candies  are  often  dipped  in  varnish  to  prevent  the  ac- 
tion of  the  air.  Formalin  is  sometimes  put  into  milk 
to  prevent  souring.  No  food  so  treated  is  good  to  eat. 

The  best  and  most  harmless  chemical  preservatives 
are  those  discovered  long  ago.  They  are  common  salt, 
vinegar,  spices,  and  wood  smoke  which  is  used  for  pre- 
serving meat.  Spices,  however,  should  be  used  sparingly. 

Wood  is  protected  by  such  compounds  as  varnish  and 
paint.  Linseed  and  poppy-seed  oils  are  the  best.  Tur- 
pentine is  used  to  make  the  paint  dry  rapidly.  Iron 
and  lead  oxides  are  used,  but  the  lead  paints  are  the  best 
if  used  with  good  linseed  oil.  The  oil  is  a  preservative, 
and  the  thin  coat  of  lead  and  dried  oil  on  the  surface 
prevents  water  and  air  from  entering  the  wood.  Rail- 
road ties  and  street  paving-blocks  are  soaked  in  an  oily 
solution  of  creosote.  Creosote  is  a  poison  and  so  prevents 
the  growth  of  any  organisms  in  the  wood.  Iron  and 
other  metals  when  exposed  to  the  air  and  moisture  are 
oxidized  and  form  rust.  This  is  prevented  by  covering 
them  with  lead  paint  or  coal  tar.  The  coal  tar  is  used  on 
bridges  made  of  steel,  as  it  is  a- very  cheap  preservative. 

QUESTIONS  AND  EXERCISES 

1.  Examine  all  kinds  of  wooden  posts  and  determine  where  they 
decay  most  rapidly.     Explain.     How  can  decay  be  prevented? 

2.  Make  a  list  of  the  diseases  in  your  community  caused  by 
germs.     What  remedies  are  used  for  some  of  them? 

3.  Name  some  good  disinfectants  and  tell  how  to  use  them. 

4.  Moisten  a  small  piece  of  bread,  roll  it  a  yard  or  more  on  the 
floor,  keep  it  moist  and  at  room  temperature  for  three  or  four  days, 
and  observe  what  happens.     Explain. 

5.  Are  your  parents  careful  about  the  kind  of  preserved  foods 
which  they  buy?     Why? 


CHAPTER   VI 
HABIT-FORMING    AGENTS 

26.  Dr.  Harvey  W.  Wiley,  formerly  chief  agricultural 
chemist  of  the  United  States,  is  an  authority  on  the 
subject  of  habit-forming  agents.  He  said :  "  Either  through 
neglect,  carelessness,  or  consent  of  parents  and  teachers, 
thousands  of  school  children  are  becoming  addicted  to 
drug  habits.  ...  In  addition  to  these  drugs,  many  chil- 
dren are  allowed  to  drink  tea  and  coffee,  and  thus  take  into 
their  systems  an  alkaloid,  caffein,  which  has  the  tendency 
to  take  away  the  sense  of  fatigue,  stimulate  the  heart's 
action,  and,  in  general,  to  urge  the  child  forward  to  greater 
physical  and  mental  activity  than  he  should  be  called 
upon  to  endure.  In  the  normal  child  the  brain  and 
body  give  timely  notice  of  fatigue;  in  the  abnormal 
child,  fed  partly  on  tea  and  coffee,  these  danger  signals 
are  struck  down,  and  the  child  has  no  sense  either  of 
physical  or  mental  fatigue.  Thus  he  keeps  on  working 
when,  if  nature  had  her  way,  he  should  be  resting.  Physi- 
cians and  teachers  should  combine  to  urge  upon  parents 
the  desirability  of  not  allowing  school  children  to  use 
tea  or  coffee. 

"In  addition  to  these  drugs  containing  caffein  there 
are  about  a  hundred  so-called  soft  drinks  on  the  market 
of  the  country,  sold  under  different  names,  to  which  caffein 
has  been  added  so  as  to  make  the  beverage,  when  con- 
sumed, have  about  the  same  quantity  of  caffein  that 


HABIT-FORMING  AGENTS  41 

tea  and  coffee  contain.  Coca  Cola  is  a  type  of  these 
beverages,  and  it  is  sold  near  schoolhouses  in  hundreds 
of  the  cities  of  this  country.  To  what  extent  the  chil- 
dren patronize  these  caffeinated  drinks  cannot  be  de- 
termined accurately,  but  that  they  do  patronize  them  is 
well  known.  Teachers  and  parents  should  join  in  their 
efforts  to  prevent  children  of  school  age  from  indulging 
in  these  very  threatening  beverages.  They  are  of  a 
character,  as  the  phrase  runs,  to  get  on  your  nerves,  and 
should  be  rigidly  excluded." 

27.  Stimulants.  —  Stimulants  are  drugs  that  increase 
heart  and  nervous  activity,  and  relieve  the  sense  of  fatigue. 
A  person_can  easily  be  overworked  under  the  influence  of 
a  stimulant  because  the  tired  feeling  cannot  appear. 
Because  of  this  fact  many  children  do  not  grow  as  they 
should  and  therefore  become  stunted  for  life,  both  in 
mind  and  body.  Proper  rest  is  just  as  necessary  as 
exercise  and  should  be  taken  when  the  sense  of  fatigue 
comes.  Fatigue  is  the  signal  given  by  the  nervous 
system  for  rest.  If  this  signal  is  broken  down  by  the 
use  of  stimulants,  a  wrecked  life  can  be  expected  and  the 
extent  of  the  wreck  will  depend  on  the  kind  and  amount 
of  stimulant  used.  There  are  times  when  stimulants  are 
necessary  to  save  lives,  but  at  such  times  the  persons  are 
sick  or  have  suffered  from  some  accident.  Stimulants 
should  be  taken  only  under  the  direction  of  a  competent 
physician. 

The  three  common  stimulants  are  tea,  coffee,  and  cocoa. 
They  all  contain  the  stimulants  known  as  alkaloids. 
Tea  contains  caffeine  or  theine.  Coffee  contains  caffeine. 
Cocoa  contains  theobromine.  The  effects  produced  by 
these  three  are  very  similar.  The  ordinary  drinks  made 
from  tea,  coffee,  and  cocoa  contain  from  one  to  two 


GENERAL  SCIENCE 


per  cent  of  the  alkaloids.  But  in  these  small  amounts 
it  is  well  known  that  they  greatly  affect  the  nervous 
system. 

Tea  and  coffee  have  practically  no  food  value,  but 
cocoa  contains  some  nutritious  fats  and  carbohydrates 
(starch  and  sugar)  and  so  cocoa  is  the  least  harmful  of 
the  three.  But  enough  fats  and  carbohydrates  can  be 
obtained  from  foods  in  which  there  is  no  stimulant. 

28.  Narcotics.  —  Narcotics  are  drugs  which  deaden 
the  nerve  sense  and  usually  hinder  proper  heart  action. 
In  large  doses  they  cause  sleep.  In  any  quantity,  how- 
ever small,  they  weaken  brain 
and  muscular  energy.  For  this 
reason  they  should  never  be 
taken  except  when  given  by  a 
competent  physician.  The  three 
common  narcotics  are  nicotine, 
alcohol,  and  opium  in  its  vari- 
ous forms.  Boys  contracting 
the  drug  habit  usually  follow 
these  up  in  the  order  named. 

Nicotine.  —  Nicotine  (CiaHu 
N2)  is  the  narcotic  found  in 
tobacco.  It  is  a  colorless  liquid 

and  is  such  a  strong  poison  that  one  drop  of  it  will  kill 
a  dog.  Nicotine  boils  at  a  temperature  of  476°  F.  (247°  C) 
and  during  the  burning  of  the  tobacco  in  smoking  the  heat 
turns  the  nicotine  into  steam  or  vapor  and  it  is  then  drawn 
into  the  mouth,  sometimes  into  the  lungs,  and  a  part  of 
it  blown  out  through  the  nose.  As  soon  as  the  smoke 
gets  into  the  mouth  or  lungs  its  temperature  is  lowered 
and  the  nicotine  soon  condenses  into  the  liquid  form  and 
is  then  absorbed  by  the  blood.  Nicotine  is  the  poison 


TOBACCO  PLANT 


HABIT-FORMING  AGENTS  43 

which  makes  boys  sick  the  first  time  they  use  tobacco. 
Cigarettes  are  usually  made  of  poor  tobacco  dipped  in  a 
solution  of  nicotine  and  other  narcotics,  often  some  form 
of  opium.  These  additional  narcotics  in  cigarettes  are 
"as  harmful  to  the  users  of  them  as  the  nicotine. 

Smokers  in  high  school  and  college  rank  on  the  average 
from  10  per  cent  to  25  per  cent  lower  in  their  studies  than 
the  non-smokers.  In  college  the  percentage  of  smokers 
who  take  athletic  honors  and  scholarships  is  lower  than 
that  of  non-smokers.  "As  a  rule,  the  non-smoker  is 
mentally  superior  to  both  the  occasional  and  the  habitual 
smoker."  (Edwin  C.  Clarke.) 

Alcohol  is  made  by  the  yeast  plant.  The  process 
is  known  as  fermentation.  Alcohol  is  in  all  •  fermented 
and  distilled  liquors  and  is  the  active  principle  that 
causes  intoxication  or  drunkenness.  Distilled  liquors  or 
whiskeys  are  made  by  distilling  fermented  grains  and 
fruits.  They  contain  from  40  per  cent  to  60  per  cent  of 
alcohol.  Fermented  drinks  are  made  by  allowing 
various  fruit  juices  to  ferment.  They  contain  from  5 
per  cent  to  14  per  cent  of  alcohol.  Sometimes  alcohol  is 
added  to  wines  and  so  they  may  contain  25  per  cent  of 
alcohol.  Malt  liquors,  such  as  beer,  are  made  by  allow- 
ing yeast  to  ferment  barley  mixed  with  hops.  They 
contain  from  3  per  cent  to  5  per  cent  of  alcohol.  The  per 
cent  of  alcohol  in  root  beer,  usually  a  homemade  drink, 
depends  on  the  amount  of  yeast  used  and  the  time  per- 
mitted for  fermentation.  Many  of  these  drinks,  sold  by 
the  saloons  and  sent  out  by  the  distillers  to  the  con- 
sumers, are  adulterated  with  narcotics  which  are  more 
injurious  than  alcohol  itself. 

The  best  physicians  of  the  world  have  said  that  alcohol 
is  a  narcotic  poison  even  in  the  smallest  amounts  and 


44 


GENERAL  SCIENCE 


therefore  should  be  dealt  with  as  other  poisons  and  its 
general  sale  prohibited. 

Opium  and  Other  Narcot&s. — The  various  forms  in 
which  opium  is  used  are:  morphine  (Ci7Hi903N),  co- 
deine (Ci8H2iN03),  narcotine  (C22H2307N),  and  heroin. 

Laudanum  is  a  mixture  of 
opium  and  alcohol.  Most  of 
the  opium  fiends  use  opium  in 
the  form  of  morphine.  Codeine 
and  morphine  are  used  in  some 
patent  cough  remedies  and 
soothing  sirups.  Cocaine 
(Ci7H2i04N)  is  taken  from  coca 
leaves  and  is  used  to  relieve 
pain. 

29.  Patent  Medicines. 
The  kinds  of  patent  medicines 
on  the  market  are  numerous 
and  nearly  all  contain  alcohol. 
Many  of  them  contain  more  alcohol  than  do  strong 
wines,  while  some  have  as  much  as  poor  whiskey.  They 
are  advertised  for  every  kind  of  petty  ill,  but  they 
only  benumb  the  nerves,  thus  making  the  danger  greater 
instead  of  effecting  a  cure.  Some  persons  who  would 
not  think  of  taking  beer,  wine,  whiskey,  or  any  other 
intoxicating  drink  consume  patent  medicines  containing 
large  quantities  of  alcohol  and  thus  thoughtlessly  expose 
themselves  to  mental  and  physical  danger.  In  case  of 
any  physical  disorder,  serious  accident,  or  disease,  the 
family  physician  should  be  consulted. 

30.  Headache  Powders.  —  On  account  of  carelessness 
in  the  habits  of  exercise,  rest,  and  eating,  a  great  number 
pf  ills,  of  varying  degrees  of  severity,  are  developed. 


OPIUM  POPPY 


HABIT-FORMING  AGENTS  45 

Headache  is  one  which  is  a  frequent  but  unwelcome 
visitor.  The  sufferer  usually  tries  to  get  rid  of  it  as  soon 
as  possible  and  in  any  way  possible,  and  will  resort  to 
drugs  from  time  to  time  instead  of  attempting  to  remove 
the  cause  by  living  a  hygienic  life.  For  such  careless 
persons  there  are  on  the  market  several  drugged  head- 
ache powders,  which  contain  acetanilid,  acetphenetidin, 
antipyrin,  caffeine,  etc.  These  compounds  are  habit- 
forming  drugs  and  should  never  be  used.  Codeine  and 
morphine  are  also  used  in  some  powders.  These  remedies 
in  general  simply  benumb  or  stupefy  the  senses,  and  do 
not  remove  the  cause  of  the  trouble. 

31.  Cold  and  Cough  Remedies.  —  Colds  and  coughs 
are  among  the  most  common  ailments  of  children,  and 
many  special  mixtures  have  been  prepared  and  placed 
on  the  market  for  treating  them.     These  remedies  usually 
contain  one  or  more  habit-forming  drugs,  and  some  con- 
tain   ether    and    chloroform.     Such    remedies    as    these 
should  not  be  permitted  in  the  hands  of   the   general 
public,  as  effective  cough  and  cold  medicines  can  easily 
be  prepared  without  the  use  of  such  drugs. 

32.  Soothing  Sirups.  —  A  host  of    drugs  have  been 
prepared   for   all   the   ills  of  early  childhood.     Careless 
mothers  give  these  remedies   to    their  children  without 
much  or  any  hesitation.     As  soon  as  the  effects  of  one 
dose  pass  away,  the  child  becomes  irritable  and  fretful. 
Another  dose  is  administered,   the  craving  is  met,  and 
the    child    is    quieted.      This   is    a    condition    which   is 
similar  in  every  respect  to  the  drug  habit  among  grown 
people. 

The  remedy  for  the  use  of  such  drugs — habit-forming 
agents — is  education  and  their  removal  from  the  market. 


46  GENERAL  SCIENCE 

QUESTIONS  AND  EXERCISES 

.  1.   Make  a  list  of  all  of  the  "soft  drinks"  of  which  you  know. 
Which  contain  caffeine  or  other  drugs,  and  which  do  not? 

2.  Enumerate  all  of  the  good  results  derived  from  the  use  of 
soft  drinks. 

3.  Enumerate  all  of  the  bad  results  derived  from  the  use  of  soft 
drinks. 

4.  Now  compare  the  two  lists  of  results.     What  is  your  con- 
clusion? 

5.  Determine  how  much  money  you  spend  every  year  for  soft 
drinks.     Is  it  wisely  spent? 

6.  Observe  whether  children  who  use  tea  or  coffee  are  as  healthy 
and  have  as  pleasant  dispositions  as  those  who  do  not  use  tea  or 
coffee. 

7.  Observe  whether  tea  and  coffee  affect  the  health  and  "temper" 
of  parents. 

8.  Consult  some  good  physiology  for  the  effects  of  stimulants  on 
children. 

9.  Notice  what  effects  narcotics,  such  as  tobacco,  alcohol,  opium, 
etc.  have  upon  those  who  use  them. 

10.  Is  the  man  who  uses  alcoholic  drinks  as  good  a  home-maker 
as  other  men? 

11.  Make  a  list  of  "patent  medicines,"  sold  in  drug  stores,  that 
contain  one  or  more  narcotics.     What  do  you  think  about  the  use  of 
such  medicines? 


CHAPTER   VII 
OXYGEN   AND    OXIDATION 

33.  The  Air  which  we  try  to  keep  pure  in  our  room 
and  which  we  breathe  is  composed  of  several  gases  which 
are  thoroughly  mixed.     These  gases  are  nitrogen,  oxygen, 
carbon    dioxide,    and    a    few   others    which    are    not   so 
useful  to  man.     Evaporated  water  is  in  the  air  in  varying 
amounts  and  is  very  necessary  for  health.     A  person  can- 
not study  well  in  a  room  where  the  air  is  too  dry.     How 
can  we  keep  the  air  from  getting  too  dry  for  health? 

The  three  important  gases  that  make  up  about  99  per 
cent  of  the  air  do  not  vary  much  in  amount.  Each  one 
is  always  present  in  about  the  same  per  cent  where  the 
air  is  unconfined  and  free  to  move  about  as  wind. 
Nitrogen  composes  about  79  per  cent  of  the  air,  and  its 
use,  as  far  as  oxidation  is  concerned,  is  to  dilute  the  oxy- 
gen and  prevent  too  rapid  burning.  Carbon  dioxide 
composes  about  .03  per  cent  of  the  air  and  is  formed  by 
burning  coal,  gas,  or  wood.  Oxygen,  which  composes 
about  20  per  cent  of  the  air,  is  the  gas  that  is  necessary 
in  the  process  of  burning  and  of  breathing. 

34.  Preparation   of   Oxygen.  —  Weigh   out   about   six 
grams    of    potassium    chlorate    (KC1O3)    and    the    same 
amount  of  manganese  dioxide  (MnO2).     Mix  these  two 
compounds  in  powdered  form  on  paper  and  place  the 
mixture  in  a  test  tube.     Have  the  test  tube  perfectly 
dry  inside  and  outside.     Close  the  test  tube  by  a  rubber 


48 


GENERAL  SCIENCE 


stopper  with  a  glass  tube  through  it  as  shown  in  the  illus- 
tration, letting  the  other  end  of  the  glass  tube  extend 
under  the  mouth  of  a  bottle  on  the  shelf  in  the  pneumatic 
trough.  Fill  several  large-mouthed  bottles  with  water, 
cover  with  a  glass  plate,  and  invert  them  on  the  shelf 
of  the  pneumatic  trough  over  a  hole;  then  remove  the 
glass  plate.  With  a  Bunsen  burner  held  in  the  hand, 


PREPARING  OXYGEN 

By  heating  a  mixture  of  equal  amounts  of  potassium  chlorate  and 
manganese  dioxide. 

apply  heat  to  the  test  tube  very  carefully;  see  that  the 
flame  does  not  stay  in  one  place,  and  that  the  entire  end 
of  the  test  tube  containing  the  compounds  is  equally 
heated,  or  the  test  tube  may  be  broken  and  then  all  the 
oxygen  will  escape  without  going  into  the  bottle.  The 
first  gas  that  comes  from  the  test  tube  through  the  de- 
livery tube  is  air  and  should  be  allowed  to  escape  before 
placing  the  end  of  the  delivery  tube  under  the  inverted 
bottle.  As  the  bottles  are  filled  with  gas  the  water  will 
flow  out  because  of  its  own  weight.  When  a  bottle  is 


OXYGEN  AND  OXIDATION  49 

filled  with  oxygen  gas  it  can  be  removed  from  the  shelf 
by  slipping  a  glass  plate  under  its  mouth  while  still  in 
the  water;  it  can  then  be  placed  on  the  desk  in  an  up- 
right position.  Leave  the  bottle  covered  to  prevent  any 
possible  mixture  of  the  oxygen  with  the  air.  This  will 
permit  the  filling  of  as  many  bottles  as  desired.  To  pre- 
vent the  breaking  of  the  test  tube,  remove  the  delivery 
tube  from  the  water  before  you  take  the  flame  away  from 
the  test  tube.  Why? 

Properties  of  Oxygen  Gas. —  Put  into  a  bottle  of  oxygen 
gas  a  splinter  of  wood  with  a  glowing  spark  on  the  end, 
and  note  the  result,  (i)  Oxygen  supports  combustion 
or  burning.  (2)  It  will  stay  in  the  upright  uncovered 
bottle,  and  will  flow  out  if  the  bottle  is  inverted;  hence 
it  is  heavier  than  air.  (3)  It  is  tasteless,  colorless,  and 
odorless.  Try  it  and  see. 

35.  Oxidation.  —  Oxidation  is  a  process  in  which  the 
atoms  of  oxygen  unite  with  the  atoms  of  other  substances 
to  form  new  compounds.  Oxidation  liberates  a  great 
amount  of  heat.  The  heat  energy  necessary  to  draw 
trains,  drive  automobiles,  keep  our  houses  and  bodies 
warm,  all  comes  from  the  burning  of  carbon  or  carbon 
compounds.  When  oxidation  occurs  so  rapidly  that  a 
flame  is  produced,  it  is  commonly  called  burning,  as  coal 
or  gas  burns  in  a  stove  or  furnace. 

We  saw  in  §  34  that  oxygen  supports  combustion  or 
burning.  The  great  quantity  of  oxygen  in  the  air  is  one 
source  of  its  supply.  The  earth  itself  is  composed  of  about 
45  per  cent  of  oxygen.  With  all  of  the  great  fires  that  we 
have  in  factories,  in  machines,  and  in  buildings  to  produce 
heat  energy,  the  per  cent  of  oxygen  and  carbon  dioxide 
of  the  out-door  air  does  not  change  much.  The  reason  for 
this  is  that  plants  use  carbon  dioxide  and  liberate  oxygen 


So  GENERAL  SCIENCE 

when  they  make  starch.  Since  oxygen  in  large  amounts 
is  necessary  for  burning,  fires  will  not  burn  well  when 
they  do  not  get  enough  air  to  supply  the  oxygen.  In 
most  gas  lamps  the  gas  is  mixed  with  air  before  it  flows 
to  the  part  where  it  burns.  This  insures  more  perfect 
oxidation  of  the  gas  and  hence  a  better  light.  A  current 
of  air  is  allowed  to  flow  into  the  fire  of  a  furnace  to  supply 
oxygen.  The  gas  that  comes  from  a  fire  or  gas  lamp 
has  a  large  per  cent  of  carbon  dioxide. 

36.  Kindling  Point  and  Spontaneous  Combustion.  - 
The  kindling  point  of  a  substance  is  that  temperature 
at  which  the  substance  will  begin  to  burn  in  a  flame. 
Various  substances  have  a  different  kindling  point,  and 
the  smaller  the  amount  of  the  substance,  the  easier  it  is 
to  raise  its  temperature  to  that  point.  For  this  reason 
when  we  want  to  start  a  wood  or  coal  fire  we  place  shav- 
ings at  the  bottom  and  on  these  fine  kindling  wood  and 
then  heavier  wood,  and  finally  on  top  of  all  this  material 
we  place  larger  pieces  of  wood  or  coal.  The  burning 
match  will  raise  the  temperature  of  the  shavings  to  the 
burning  or  kindling  point,  and  they  in  turn  will  heat  /the 
kindling  wood,  and  so  on  up  to  the  kindling  temperature 
of  the  largest  wood  or  coal.  When  wood  or  coal  is  heated 
to  the  kindling  point  a  gas  escapes,  and  the  burning  of 
this  gas  is  what  makes  the  flame.  Sometimes  hay  in  a 
barn  or  old  rags  and  paper  stored  in  sheds  or  closets, 
become  so  hot  that  the  kindling  temperature  is  reached, 
and  the  whole  building  containing  the  material  will  burst 
into  flame;  this  is  called  spontaneous  combustion. 

The  ancient  method  of  raising  wood  to  the  kindling 
temperature  was  by  friction,  that  is,  by  rubbing  two 
sticks  together  till  they  caught  fire.  The  American 
Indians  used  this  method.  Then  came  into  use  the 


OXYGEN  AND  OXIDATION 


TINDER 


Box,    FLINT,    AND 
STEEL 


flint-stone  and  steel,  by  which  a  spark  was  ms,de  to  fly 
on  fine  kindling  material  called  "tinder."  During  the 
Colonial  days  of  America  fire  was  also  carried  in  earthen 
buckets  from  house  to  house. 
During  the  second  quarter  of 
the  nineteenth  century  the  first 
form  of  our  modern  match  came 
into  use. 

37.  Friction  Matches. - 
Matches  are  made  to  be  used  in 
the  same  general  way  as  the 
ancient  method  of  making  fire 
by  friction.  The  difference  is  that  the  match  is  made 
of  material  with  a  low  kindling  temperature.  One 
stroke  of  the  match  on  the  proper  surface  will  produce 
enough  heat  to  raise  it  to  the  kindling  point  and  so  it 
burns  into  a  flame.  The  match  is  made  of  pine,  dipped  in 
oil,  and  then  into  a  mixture  of  phosphorus,  sulphur,  and 
glue.  The  phosphorus  has  a  low  kindling  point  and  is 
held  on  the  match-wood  by  the  glue.  The  common 
matches  were  made  of  yellow  phosphorus.  This  will 
catch  fire  in  the  air  at  a  temperature  of  95°  F.  That  is 
why  the  matches  smoke  when  held  between  the  fingers. 
Yellow  phosphorus  is  also  extremely  poisonous.  Because 
matches  made  of  this  phosphorus  are  dangerous,  the 
safety  matches  are  very  widely  used.  Some  are  made  of 
red  phosphorus,  which  will  not  burn  till  heated  to  $00°  F. 
The  safety  match-head  commonly  contains  a  mixture  of 
potassium  chlorate,  potassium  bichromate,  powdered 
glass,  and  glue  or  dextrine  sugar.  The  friction  surface 
on  the  box  is  made  of  a  mixture  of  red  phosphorus,  anti- 
mony sulphide,  manganese  dioxide,  and  glue.  The  pow- 
dered glass  is  used  to  produce  more  friction  and  thus  make 


$2  GENERAL  SCIENCE 

it  easier  to  raise  the  temperature  of  the  match  to  the  kind- 
ling point.  Safety  matches  can  be  lighted  only  on  the  pre- 
pared surface  of  the  containing  box  or  on  plates  of  glass 
like  window  panes.  They  were  first  made  in  Swdeen. 

38.  When  any  substance  unites  with  oxygen  the 
process  is  called  oxidation.  This  may  occur  very  slowly 
and  at  a  low  temperature,  as  the  rust  on  iron  is  formed 
by  oxygen  uniting  with  the  iron,  producing  an  iron  oxide. 
Most  metals  will  unite  with  oxygen  to  form  oxides,  but 
not  so  rapidly  as  iron.  In  all  kinds  of  animal  life  oxida- 
tion takes  place,  and  the  heat  evolved  produces  the 
energy  that  enables  the  animals  to  move  about  An 
animal  could  not  move  if  oxidation  should  stop  in  its 
body.  There  are  many  one-celled,  microscopic  animals 
and  plants  which  live  by  eating  larger  dead  animals  and 
plants,  producing  what  is  commonly  called  decay.  The 
one-celled  animals  and  plants  take  in  oxygen  and  give 
off  carbon  dioxide,  and  so  when  they  eat  up  other  animals 
and  plants  the  process  which  we  think  of  as  decay  is 
really  oxidation.  When  carbon  or  its  compounds  are  oxi- 
dized, a  gas  is  formed  which  is  known  as  carbon  dioxide. 

QUESTIONS  AND  EXERCISES 

1.  Make  a  collection  of  various  kinds  of  matches.    Which  can 
most  easily  be  lighted?     Why  will  some  light  if  you  step  on  them 
and  others  will  not? 

2.  Why  will  damp  hay  in  a  barn  sometimes  ignite? 

3.  What  may  happen  if  you  store  away  a  large  pile  of  rags,  some 
of  them  oily  ones?     Why? 

4.  What  material  would  you  use  to  start  a  wood  or  coal  fire? 
How  would  you  arrange  the  material? 

5.  What  use  is  made  of  a  large  part  of  the  food  which  we  eat? 


CHAPTER   VIII 
CARBON   DIOXIDE 

39.  Carbon  and  its  Forms.  —  Carbon  is  a  simple  sub- 
stance or  element  composed  of  simple  molecules.  It 
exists  in  forms  varying  from  powdered  charcoal  to  the 
hard  crystallized  form  known  as  diamond.  It  enters 


Crystal  Rough 

DIAMONDS.  —  A  FORM  OF  CARBON 

into  the  composition  of  all  plants  and  animals,  being  one 
of  the  most  important  elements.  Our  bodies  —  the  bones 
and  flesh — are  partly  carbon,  and  the  smallest  microscopic 
animals  contain  carbon.  A  large  percentage  of  the  plants 
around  us,  such  as  the  grass,  flowers,  vegetables,  and 
trees  contain  carbon.  It  is  in  the  wood,  oil,  coal,  and  gas 
that  we  burn,  in  the  clothes  we  wear,  in  the  food  we  eat. 
We  are  kept  warm  by  the  oxidation  of  the  carbon  in  the 
food  we  eat.  Buildings  are  heated  by  oxidizing  the  car- 
bon in  the  fuel. 

Charcoal  is  one  of  the  commercial  forms  of  almost  pure 
carbon,  and  it  has  many  uses  other  than  for  fuel.  Some  is 
used  in  the  reduction  of  ores  and  purification  of  metals. 


54  GENERAL  SCIENCE 

It  is  also  widely  used  as  a  filter  for  purification  of  air, 
water,  sugar,  vinegar,  etc. 

Sewer  gases,  which  have  a  bad  odor  and  are  sometimes 
poisonous,  can  be  prevented  from  escaping  to  the  streets 
and  buildings  by  the  use  of  charcoal  filters  at  the  sewer 
exits.  As  charcoal  is  very  porous,  it  absorbs  the  poisons 
of  the  gases  and  thus  keeps  the  regions  surrounding 
sewers  clean  and  free  from  bad  odors.  Pieces  of  charcoal 
placed  in  flower  vases  will  prevent  discoloration  of  the 
water  and  absorb  the  odorous  gases  of  the  stems  that 
may  be  decaying.  Charcoal  filters  used  to  purify  drink- 
ing water  may  become  dangerous,  as  the  pores  of  the 
charcoal  may  become  filled  with  impurities,  and  thus  as 
more  water  flows  through,  it  may  become  contaminated 
instead  of  purified.  Such  filters  should  be  changed  or 
cleaned  often.  It  is  very  difficult  to  wash  the  filth  out 
of  the  filter  unless  the  charcoal  is  in  powdered  form. 
The  charcoal  may  be  purified  by  heating  it  to  redness. 
This  will  oxidize  all  the  dangerous  material  collected  in 
the  pores. 

Sugar  is  made  of  the  sap  from  the  sugar  maple  tree 
and  of  the  juice  from  the  sugar  cane  and  the  sugar  beet. 
The  raw  liquids  from  these  plants  are  boiled  down,  that 
is,  the  water  is  made  to  evaporate,  and  the  sugar  is  allowed 
to  crystallize.  This  is  known  as  raw  sugar;  it  has  a 
brown  color  and  usually  an  unpleasant  taste.  This  raw 
sugar  is  sent  to  the  sugar  refinery,  where  it  is  heated  and 
again  turned  into  a  sirup.  The  sirup  is  filtered  through 
charcoal  known  as  bone  black  or  animal  charcoal.  From 
this  filtered  sirup  the  white,  clean  sugars  on  the  market 
are  made.  The  charcoal  made  from  animals  has  a  greater 
refining  power  than  that  made  from  wood,  and  for 
this  reason  it  is  used  in  the  sugar  industry. 


CARBON  DIOXIDE 


55 


Charcoal  and  Coke  are  made  on  the  same  principle, 
namely,  by  heating  coal,  wood,  or  bones  in  an  oven  or 
any  place  to  which  air  does  not  have  free  access.  This 
prevents  enough  oxygen  from  getting  to  the  burning 
substance  to  permit  complete  or  perfect  oxidation.  But 
the  heat  produced  will  nevertheless  drive  out  the  water 
and  some  gases  and  leave  the  coke  and  charcoal. 

Wood  charcoal  used  to  be  made  by  cutting  the  wood 
in  lengths  of  about  four  or  five  feet  and  then  making  a 


WOOD  ARRANGED  FOR  BURNING  INTO   CHARCOAL 

stack  of  this  by  standing  it  on  end  and  covering  it  with 
earth  about  a  foot  deep.  An  opening  was  left  at  the 
top  for  the  gases  to  escape.  It  was  permitted  to  burn 
for  a  day  or  two  and  then  the  fire  was  put  out  by 
closing  all  openings  by  which  air  could  enter  or  smoke 
escape.  This  would  extinguish  the  fire,  because  burning 
cannot  continue  without  oxygen  and  the  escape  of  carbon 
dioxide.  After  the  fire  was  out  the  earth  covering  was 
removed  and  the  wood  charcoal  was  ready  for  market. 

A  large  percentage  of  the  soft  coal  mined  in  Pennsyl- 
vania and  neighboring  states  is  made  into  coke.  Long 
double  rows  of  brick  coke-ovens  are  made  and  filled  with 
coal.  An  opening  about  one  foot  in  diameter  is  left  at 


56  GENERAL  SCIENCE 

the  top,  through  which  the  gas  of  the  burning  coal  can 
escape.  While  the  coal  is  burning  a  large  flame  of  fire 
can  be  seen  at  this  opening.  After  the  gas  has  been 
driven  out  of  the  coal  and  burned,  a  large  hole  is  made 
in  the  side  of  the  oven  and  the  coke  is  taken  out  for 
shipment. 

40.  Preparation  of  Carbon  Dioxide.  —  Carbon  dioxide 
(062)  is  composed  of  the  two  simple  elements,  carbon  and 
oxygen.  One  atom  of  carbon  and  two  of  oxygen  make 
the  molecule  of  carbon  dioxide.  Whenever  the  oxida- 
tion of  carbon  or  its  compounds  occurs, 
carbon  dioxide  is  formed.  It  is  very  difficult 
to  get  it  in  pure  form  by  any  oxidizing  pro- 
cess, as  other  gases  are  mixed  with 
it.  So  we  shall  have  to  resort  to 
the  use  of  compounds  containing 
carbon  and  oxygen  in  the 
proper  combination  to  be 
liberated  in  the  form  of  car- 
bon dioxide  (CO2). 

If  baking  powder  is  placed 
MAKING  CARBON  DIOXIDE         in   water   or   baking   soda   in 
By  pouring  hydrochloric  acid  on    vinegar,   carbon   dioxide  will 

marble  chips.  .      ...  .       T.  .  .      .. 

be  liberated.  If  marble,  lime- 
stone, or  chalk  is  placed  in  dilute  hydrochloric  acid 
(HC1),  carbon  dioxide  will  be  evolved.  To  collect  the 
effervescing  gas,  place  the  marble  in  a  large  test  tube  or 
a  bottle,  close  it  with  a  rubber  cork  containing  a  thistle 
tube  and  a  delivery  tube.  Have  the  delivery  tube  bent 
and  long  enough  to  extend  to  the  bottom  of  a  test  tube 
or  bottle  as  shown  in  the  illustration.  Now  pour  a  little 
hydrochloric  acid  into  the  thistle  tube,  and  the  carbon 
dioxide  will  pass  out  through  the  delivery  tube  into 


CARBON  DIOXIDE 


57 


the  collecting  bottle.  As  the  carbon  dioxide  is  a  little 
heavier  than  the  air  at  the  same  temperature,  it  will 
force  the  air  out  of  the  bottle  and  will  itself  stay  in  as 
long  as  the  bottle  is  in  an  upright  position.  Can  you 
see,  taste,  or  smell  carbon  dioxide?  Carbon  dioxide  is 
not  poisonous,  but  if  it  is  breathed  in  sufficient  quantity 
it  will  cause  death  by  keeping  oxygen  out  of  the  lungs. 
41.  Uses  of  Carbon  Dioxide.  —  Some  natural  spring 
waters  are  charged  with  carbon  dioxide  and  are  called 
carbonated  waters,  such  as  are  found  at 
Colorado  Springs.  Soda  water  is  charged 
with  carbon  dioxide.  The  most  valuable 
commercial  use  of  carbon  dioxide  is  in 
the  fire  extinguisher,  various  forms  of 
which  are  on  the  market.  The  fire  extin- 
guisher used  by  fire  companies  and  known 
as  the  " chemical  wagon,"  and  smaller 
ones  for  hand  use  are  made  of  a  strong 
metal  case  containing  a  saturated  solution 
of  bicarbonate  of  soda  (baking  soda)  and 
a  glass  bottle  full  of  strong  sulphuric 
acid.  The  bottle  is  held  rigidly  in  place,  PORTABLE  FIRE 

but  the  stopper  fits  loosely.  EXTINGUISHER 

A      ,  .,  . .         .  ,          .      .  (Partly  Open) 

As  long  as  the  extinguisher   is  in  an  Showing  Stopper. 
upright  position  the   acid    stays   in   the  ed  Acid  Bottle  in 

,  c  ,  Original    Position. 

bottle  and  no  gas  is  produced,  as  the 
two  compounds  cannot  mix.  When  the  extinguisher  is 
inverted,  the  acid  escapes  from  the  bottle  into  the  soda 
solution;  chemical  action  then  takes  place  and  carbon 
dioxide  gas  is  set  free.  The  gas  produces  great  pressure 
in  the  extinguisher  and  forces  the  solution  out.  This 
carbonated  solution  is  directed  at  the  base  of  the  fire  by 
a  nozzle.  Carbon  dioxide  does  not  support  combustion, 


58  GENERAL  SCIENCE 

and  it  keeps  the  oxygen  of  the  air  away,  so  the  fire  dies 
because  it  cannot  get  sufficient  oxygen  to  make  it  burn. 
The  liquid  also  helps  to  lower  the  temperature  of  the 
burning  material  below  the  kindling  point,  thus  giving 
the  extinguisher  or  "chemical  wagon"  a  double  effect. 
It  is  only  used,  however,  when  the  fire  is  small  or 
is  just  starting.  The  way  water  extinguishes  fire  is 
by  cooling  the  burning  material  below  the  kindling 
temperature,  and  the  steam  that  is  formed  keeps  the 
air  away. 

The  carbon  dioxide  which  comes  from  the  breath  of 
all  animals  and  from  fires  used  for  heating,  lighting,  and 
power  production  would  soon  make  the  air  unfit  for  us 
to  breathe  if  it  were  not  for  a  natural  provision  for  the 
consumption  of  this  gas.  Nearly  all  plants  have  the 
power  to  make  starch  out  of  water  and  carbon  dioxide, 
when  they  grow  in  the  presence  of  sunlight.  This  starch 
is  used  by  the  plant  to  make  heat  and  wood  fiber  or 
the  body  of  the  plant.  When  the  plants  make  starch 
they  give  off  pure  oxygen.  So  the  plants  use  what  the 
animals  give  off  as  waste  and  the  animals  use  what  the 
plants  give  off  as  waste. 

QUESTIONS  AND  EXERCISES 

1.  Examine  some  hard  and  soft  coal  and  charcoal.     What  differ- 
ences do  you  find?     Of  what  are  they  chiefly  composed? 

2.  Name  all  of  the  things  produced  when  carbon  is  oxidized. 
Which  one  is  most  useful? 

3.  What  effect  has  carbon  dioxide  upon  fire?     Why? 

4.  What  effect  has  water  upon  fire?     Why? 

5.  What  commercial  uses  are  made  of  carbon  dioxide? 

6.  What  causes  bread  dough  to  rise? 


CHAPTER   IX 
BREATHING   AND    VENTILATION 

42.  Breathing.  —  From  the  chapter  on  Oxidation  we 
learned  that  a  fire  is  kept  burning  by  a  continuous  supply 
of  air  which  contains  oxygen,  and  that  the  oxidation  of 
carbon  compounds  produces  heat.  Our  bodies  are  kept 
warm  by  oxidizing  the  food  that  we  eat.  The  energy 
necessary  to  move  and  to  do  work  is  produced  in  our 
bodies  by  oxidation.  In  order  to  live,  this  oxidizing 
process  must  never  stop.  It  is  the  fire  of  life,  and  when 
it  stops  life  itself  ceases.  The  body  has  two  organs,  the 
lungs,  whose  work  it  is  to  get  oxygen  into  the  blood  for 
distribution  to  all  parts  of  the  body. 

Breathing,  then,  consists  of  the  process  of  allowing 
the  air  to  flow  into  the  lungs  and  forcing  it  out  again. 
By  the  action  of  the  muscles  of  the  chest  and  the  dia- 
phragm, the  chest  cavity  containing  the  lungs  is  enlarged 
and  the  air  flows  in  because  the  pressure  of  the  air  on  the 
outside  is  greater  than  the  pressure  of  the  air  in  the  lungs. 
Air  always  flows  to  the  place  where  the  pressure  is  least. 
When  the  lungs  are  full  of  air,  the  muscles  of  the  chest 
contract  and  force  the  air  out.  The  air  flows  out  because 
the  pressure  in  the  lungs  is  then  greater  than  the  pressure 
of  the  air  on  the  outside. 

Lamps  do  not  burn  brightly  or  fires  abundantly  if  the 
supply  of  oxygen  is  for  any  cause  insufficient.  So  it  is 
with  our  bodies.  We  shall  not  be  bright  and  happy  and 


60  GENERAL  SCIENCE 

able  to  work  and  play  unless  we  keep  a  continual  supply 
of  pure  air  flowing  into  our  lungs.  The  lungs  must 
also  be  kept  healthy  and  open  so  that  the  oxygen  may 
pass  into  the  blood.  To  insure  this  the  muscles  of  the 
chest  and  the  diaphragm  must  be  developed  and  made 
strong  by  breathing  exercises.  The  lower  part  of  the 


Increased  Air 

Space 


Inspiration  Expiration 

DIAGRAMMATIC  SECTIONS  OF  THE  BODY  IN  INSPIRATION  AND 
EXPIRATION 

chest  should  not  be  made  smaller  by  tight  clothing  such 
as  ladies  sometimes  wear.  In  this  way  serious  ill  health  is 
often  caused  in  later  life.  The  evil  results  of  tight  bands 
worn  about  the  waist,  especially  by  young  girls,  frequently 
continue  to  make  the  life  of  the  victim  miserable  to  its  end. 
43.  Mouth  Breathing.  —  We  sometimes  see  children 
and  adults  continuously  breathing  through  the  partially 
open  mouth.  Notice  yourselves  to  see  if  you  are  doing 
this.  The  mouth  was  not  made  for  the  purpose  of 
taking  air  into  the  lungs,  but  the,  nose  was.  People 


BREATHING  AND  VENTILATION  61 

breathe   through  the   mouth  from   one  or  more  of   the 

following  causes:    (i)  They  may  have  abnormal  spongy 

growths  in  the  back  part  of  the  nose.     These  are  called 

adenoids.     They  keep   the   air  from   going   through  the 

nose,    and    so    the    child    who 

has  them  is  compelled  to  open 

its  mouth  to  get  air.     In  ad- 

dition, adenoids  interfere  with 

the  flow  of  blood  to  the  brain 

and    cause    indistinct    pronun- 

ciation   of    words,   listlessness, 

inattention,  poor  memory,  par-  ADENOIDS 


tial  deafness,  and  frequent 
colds,  or  earache.  The  signs 
indicating  the  presence  of  adenoids  are  parted  lips, 
prominent  eyeballs,  a  narrow,  high-arched  roof  of  the 
mouth,  and  nasal  speech.  Adenoids  can  easily  be  re- 
moved by  a  physician.  (2)  Colds  and  catarrh  cause 
the  nose  to  be  clogged  by  the  slimy  fluid  secreted  by 
the  mucous  membrane,  so  the  air  cannot  easily  pass 
through.  (3)  Carelessness  and  indifference  on  the  part 
of  many  are  also  causes  of  mouth  breathing. 

44.  Effects  of  Mouth  Breathing.  —  (a).  The  mouth 
passage  is  much  shorter  for  the  flow  of  air  than  by  way 
of  the  nose,  so  the  air  breathed  through  the  mouth  is  not 
warmed  before  reaching  the  throat  and  lungs  and  hence 
irritates  the  vocal  cords  and  causes  coughing,  and  finally 
a  husky  voice  will  result.  In  cool  weather  colds  may  re- 
sult from  mouth  breathing,  (b)  The  mouth  does  not 
strain  out  the  dust  and  germs  as  the  hairs  and  mucous 
folds  in  the  nose  do,  and  so  the  throat  and  lungs  become 
irritated  and  diseases  may  be  contracted  from  the  inhaled 
germs.  The  dust  in  the  lungs  will  also  hinder  the  flow 


62  GENERAL  SCIENCE 

of  oxygen  into  the  blood  and  the  flow  of  carbon  dioxide 
out  of  the  blood.  It  also  makes  the  lungs  less  able  to 
resist  disease,  (c)  Mouth  breathing  causes  a  narrowing 
of  the  upper  jawbone  and  the  teeth  may  protrude  forward 
and  not  have  enough  space  for  healthy  growth.  This  in 
later  life  will  cause  the  person  to  have  continually  an 
open  mouth,  (d)  Mouth  breathing  causes  improper 
enunciation  of  words  and  a  harsh  tone  due  to  injured 
vocal  cords.  A  mouth  breather  can  never  have  a  good 
voice  for  singing. 

45.  Nose    Breathing.  —  (a)  By  inhaling   through   the 
nose  the  air  is  warmed  and  irritation  of  the  throat  and 
lungs  is  prevented,     (b)  Most  of  the  dust  and  germs  are 
taken  out  of  the  air  before  it  reaches  a  place  where  injury 
might  be  done,     (c)  The  air  is  moistened  and  so  the  throat 
is  not  irritated  by  dryness.     (d)  Colds  are  not  so  easily 
caught  as  by  mouth  breathing,     (e)  It  permits  the  proper 
development  of  the  face  and  avoids  other  evils  of  mouth 
breathing. 

Deep  breathing  exercises  should  be  practiced  daily  to 
cause  the  air  to  go  to  every  part  of  the  lungs  and  keep 
them  open  and  also  to  develop  the  breathing  muscles. 
Boys  should  never  smoke,  because  tobacco  smoke  con- 
tains two  dangerous  poisons,  namely,  nicotine  and  carbon 
monoxide,  which  affect  the  whole  air  passage  by  irritating 
the  mucous  membrane,  besides  getting  these  poisons  into 
the  blood. 

46.  Ventilation.  —  Ventilation  consists   of   keeping  in 
our  homes  and  buildings  a  supply  of  pure  air  for  breath- 
ing.    When  it  goes  into  our  lungs,  the  air  if  pure  contains 
about  20  per  cent  of  oxygen  and  about  .03  per  cent  of  car- 
bon dioxide.     When  it  comes  out  of  the  lungs  it  is  impure 
air  and  contains  about  16  per  cent  of  oxygen  and  4.03  per 


BREATHING  AND  VENTILATION 


WINDOW  VEN- 
TILATION WITH- 
OUT DRAFTS 


cent  of  carbon  dioxide.  Gas-lights  and  open  fires  consume 
much  oxygen  and  give  off  carbon  dioxide.  To  remove  the 
carbon  dioxide  produced  by  breathing  and 
by  lights  and  fires,  and  to  keep  a  continu- 
ous supply  of  oxygen,  it  is  necessary  to  have 
openings  for  the  air  to  enter  our  rooms. 
Each  person  should  have  about  300  cubic 
feet  of  fresh  air  every  hour.  Gas-lights 
and  fires  need  more.  In  an  ordinary- 
sized  room  of  a  home  10,000  cubic  feet  of 
air  can  be  allowed  to  enter  each  hour 
without  danger  of  a  draft.  Air  must  move 
three  or  more  feet  per  second  before  it  can 
be  felt  as  a  draft.  If  air  is  moving  three 
feet  per  second  through  an  opening  with  an  area  of  one 
square  foot,  10,800  cubic  feet  of  air  would  enter  each 
hour.  Where  there  is  no  system  of  ventilation  in  a 
building,  the  windows  should  be  lowered  from  the  top, 
or  the  lower  sash  raised  and  a  board  placed  under  it  so 
that  the  air  will  have  to  come  in  between  the  two  sashes, 
thus  giving  it  an  upward  direction.  The  windows  of 
sleeping  rooms  should  be  kept  open  when  they  are 
occupied. 

QUESTIONS  AND   EXERCISES 

1.  Compare  the  chest  and  shape  of  the  shoulders  of  those  who 
take    breathing  exercises  and  those  who  do  not. 

2.  Observe  those  who  breathe  through  the  mouth  and  see  how 
it  affects  their  appearance. 

3.  What  should  be  done  if  children  are  found  breathing  through 
the  mouth? 

4.  Who  is  more  liable  to  get  dust  and  disease  germs  into  his 
lungs,  one  who  breathes  through  the  mouth  or  through  the  nose? 

5.  How  do  you  ventilate  your  home?     Your  sleeping  room? 


CHAPTER  X 
MATTER   AND    ENERGY 

47.  Matter.  —  Matter  or  material  is  that  which  we 
think  of  as  having  weight  or  mass.  Such  materials  as 
wood,  rock,  iron,  books,  water,  air,  etc.  are  what  we 
think  of  as  matter.  From  previous  chapters  we  have 
learned  that  substances  may  undergo  a  number  of  changes. 

For  instance,  the  interaction  of  a  base  and  an  acid 
brought  about  a  change  (§13)  by  which  both  base  and  acid 
were  destroyed,  but  the  material  composing  them  was 
not  destroyed.  The  weight  of  the  salt  and  water  formed 
by  the  action  of  hydrochloric  acid  on  caustic  soda  (§13)  is 
the  same  as  the  combined  weights  of  the  acid  and  the 
base  used.  When  coal  is  burned  the  combined  weight 
of  the  carbon  dioxide  and  other  gases  formed  and  the 
ashes  left  is  the  same  as  the  combined  weight  of  the  coal 
and  oxygen  used  to  burn  it.  We  can  take  a  board  and 
cut  it  into  pieces  and  make  a  box  of  it,  and  the  weight 
of  the  box  will  be  the  same  as  that  of  the  board  less  the 
weight  of  the  sawdust  and  the  pieces  wasted. 

We  have  seen  many  kinds  of  transformations  of  matter, 
but  in  no  case  was  it  destroyed.  Its  use  to  man  may 
have  been  destroyed,  but  not  the  material;  as  when  a 
wagon  is  wrecked,  its  usefulness  is  gone,  but  the  material 
of  which  the  wagon  was  made  still  exists.  From  our  ex- 
periences with  matter  we  could  say  that  matter  cannot  be 
destroyed,  but  its  form  and  appearance  can  be  changed. 


MATTER  AND  ENERGY  65 

We  also  might  add  that  matter  cannot  be  created  by 
man.  If  you  think  it  can  be  created,  make  some  salt, 
or  carbon  dioxide,  or  a  chair,  without  taking  any  material 
out  of  which  to  make  it.  We  can  change  the  form  of 
matter,  but  we  cannot  create  or  destroy  it.  The  law  of 
the  conservation  of  matter  is:  Matter  cannot  be  destroyed 
or  created,  but  can  be  transformed. 

48.  States  of  Matter.  —  There  are  three  forms  or 
states  in  which  matter  exists,  namely,  solids,  liquids, 
and  gases.  The  molecules  of  which  all  material  is  com- 
posed are  moving  rapidly,  and  they  are  never  perfectly 
at  rest. 

When  matter  is  in  the  form  called  a  solid,  as  ice  and 
iron  are  at  ordinary  temperatures,  the  molecules  are  held 
within  a  given  space  by  the  force  of  attraction  which 
they  have  for  one  another.  They  cannot  move  enough 
to  change  the  shape  of  the  solid,  commonly  speaking. 

When  the  molecules  are  made  active  by  the  application 
of  sufficient  heat,  their  speed  becomes  so  great  that  much 
of  the  force  of  attraction  which  they  have  for  one  another 
is  overcome;  then  the  molecules  of  matter  form  what  is 
known  as  a  liquid.  In  liquids  the  molecules  move  over 
or  about  one  another  with  such  speed  and  ease  that  the 
liquid  will  take  the  shape  of  the  vessel  containing  it. 
The  reason  that  liquids  can  be  poured  from  one  vessel  to 
another  is  because  of  the  ease  with  which  the  molecules 
move. 

If  sufficient  heat  is  applied  to  matter  in  the  liquid 
state,  the  molecules  become  so  active  and  move  about 
with  such  speed  that  the  force  of  attraction  which  they 
have  for  one  another  is  completely  overcome,  and  they 
continue  to  bounce  about  like  a  tennis  ball  batted  by  two 
players.  Matter  in  this  state  is  called  a  gas.  Any  quantity 


66  GENERAL  SCIENCE 

of  gas  placed  in  a  closed  vessel  will  take  the  shape  of  the 
vessel  and  also  fill  it,  because  the  molecules  move  in 
every  direction  with  great  speed.  It  is  the  continuous 
hammering  of  these  millions  of  molecules  on  the  sides  of 
the  containing  vessel  that  produces  what  is  known  as 
gas  pressure.  The  pressure  due  to  the  molecules  of  a 
gas  hitting  the  sides  of  the  vessel  or  gas  pipe  could  be 
illustrated  by  letting  a  stream  of  small  lead  shot  fall  on 
a  balance  scales.  It  would  be  found  that  the  force  of 
the  stream  of  shot  would  be  proportional  to  the  number 
of  shot  striking  the  balance  per  second,  if  their  speed  is 
kept  constant,  which  could  be  done  by  permitting  them 
to  fall  from  the  same  height.  The  pressure  of  a  gas  is 
proportional  to  the  number  of  molecules  striking  the 
sides  of  the  containing  vessel  per  second,  if  their  speed  is 
kept  constant.  Their  speed  is  dependent  upon  their 
temperature. 

From  the  chapter  on  Chemistry  of  Common  Things  we 
learned  that  all  matter  is  composed  of  molecules.  Com- 
plex molecules  are  composed  of  two  or  more  atoms. 
Atoms  are  composed  of  electrons  or  ions.  By  great  scien- 
tists, such  as  Professors  Millikan  and  J.  J.  Thompson,  it 
has  been  found  that  the  electron  is  only  a  charge  of  elec- 
tricity, and  when  the  electric  charge  is  removed  no  weight 
is  left.  Hence  atoms  are  composed  of  a  number  (varying 
from  700  in  hydrogen  to  160,000  in  radium)  of  electrical 
charges  so  arranged  that  they  are  not  easily  moved  out  of 
their  sphere  of  activity.  Atoms  compose  molecules,  and 
hence  molecules  are  composed  of  charges  of  electricity. 
All  matter  is  composed  of  molecules;  therefore,  matter  is 
electricity. 

49.  Gravity.  —  Gravity  is  the  force  with  which  the 
earth  draws  objects  toward  its  center  or  holds  objects 


MATTER  AND   ENERGY 


67 


on  its  surface.  This  force  is  what  gives  objects  weight; 
it  causes  objects  to  fall  toward  the  earth.  When  a  ball 
is  thrown  up,  gravity  stops  it  and  draws  it  back  to  the 
earth's  surface.  It  was  Sir  Isaac  Newton  who  first 


explained  why  unattached  objects  fall. 

The  earth's  attraction  can  be  illus- 
trated by  the  use  of  a  magnet  and  an 
iron  nail.  A  magnet  is  a  piece  of  steel 
with  its  molecules  so  arranged  that  it 
can  draw  small  pieces  of  iron  to  itself, 
and  yet  there  is  no  kind  of  connection 
between  the  magnet  and  the  piece  of 
iron.  When  the  nail  touches  the  mag- 
net it  will  adhere  to  the  magnet  much  as 
an  object  is  held  to  the  earth  by  gravity. 

All  bodies  —  •  the  sun,  moon,  stars, 
and  even  apples,  balls,  and  stones  — 
have  the  power  of  attracting  other 
bodies  toward  them.  This  general  force 

1.111.  e 

of  attraction  which  bodies  have  for  one 

another  is  called  gravitation.      Gravitation  can  be 


Two  BALLS 


influence 

tation. 


of  gravi- 


illus- 


trated by  suspending  with  long  strings  a  large  lead  ball 
near  a  small  brass  ball.  The  brass  ball  will  be  drawn 
aside  from  a  vertical  position,  or  the  distance  between 
the  strings  near  the  balls  will  be  found  to  be  less  than  it 
is  at  the  point  of  suspension.  Gravitation  is  a  property 
of  matter,  and  it  is  the  force  of  gravitation  which  holds 
the  earth  and  all  the  other  heavenly  bodies  in  position. 
50.  Energy.  —  We  cannot  think  of  redness  or  beauty 
apart  from  some  object  or  without  having  some  object 
for  their  cause.  So  it  is  with  energy.  We  cannot  think 
of  it  except  in  connection  with  some  material  thing. 
So  we  define  it  thus:  The  energy  of  a  body  is  its  capacity 


68  GENERAL  SCIENCE 

for  doing  work.  Energy  exists  in  various  forms,  according 
to  the  kind  of  body  in  which  it  is  found,  such  as  heat 
energy,  mechanical  energy,  electrical  energy. 

Heat  energy  can  be  changed  to  mechanical  energy, 
and  mechanical  to  electrical  energy,  and  electrical  energy 
can  be  changed  back  to  mechanical  energy  and  heat. 
When  fuel  is  burned  in  the  cylinder  of  a  gas  engine  the 
energy  that  the  fuel  contains  is  transformed,  part  appear- 
ing in  the  form  of  mechanical  energy  which  does  work, 
and  a  considerable  part  taking  the  form  of  heat.  If  the 
engine  is  run  without  pulling  a  load,  all  the  energy  of 
the  fuel  used  is  changed  into  heat,  in  part  directly  in  the 
cylinder  and  in  part  through  the  heating  of  the  bearings 
by  friction.  Such  an  engine  is  spoken  of  as  a  trans- 
former of  energy  because  it  changes  one  form  of  energy 
into  another. 

The  process  in  our  bodies  is  similar  to  that  in  the  engine. 
The  materials  digested  from  our  food  are  carried  by  the 
blood  to  the  working  tissues  and  there  virtually  burned. 
Part  of  the  energy  may  be  used  to  do  visible  external 
work,  but  even  then  much  of  it  is  converted  into  the 
form  of  heat.  While  our  bodies  are  in  a  state  of  so-called 
rest,  the  work  done  by  the  internal  organs  finally  results 
in  the  generation  of  heat,  somewhat  as  does  the  motion 
of  the  engine  when  it  is  not  pulling  a  load. 

In  a  great  number  of  investigations  it  has  been  found 
that  whenever  one  form  of  energy  disappears  an  equiva- 
lent amount  appears  in  some  other  form.  Thus,  if  heat 
is  produced  by  mechanical  means,  such  as  the  fall  of  an 
object  from  a  height,  friction,  or  other  means,  the  heat 
which  appears  is  always  exactly  proportional  to  the 
mechanical  energy  used  in  producing  it.  If  the  stored-up 
energy  of  gasoline  is  used  to  run  an  engine,  the  work 


MATTER  AND   ENERGY  69 

done  plus  the  heat  produced  always  bears  the  same 
relation  to  the  energy  contained  in  the  gasoline  burned. 
When  heat  is  used  to  make  water  hot,  the  water  will 
give  out  as  much  heat  on  cooling  as  it  took  up  "in  becom- 
ing heated.  The  heat  required  to  change  water  to  steam 
is  given  out  when  the  steam  is  condensed.  This  principle 
is  used  in  steam-heating  plants. 

This  universal  experience  is  expressed  in  the  law  of  the 
conservation  of  energy,  which  may  be  stated  thus :  Energy 
can  neither  be  created  nor  destroyed,  but  it  can  be  trans- 
formed. It  may  change  its  form,  but  its  total  amount 
is  neither  increased  nor  diminished. 

If  coal  is  burned  in  a  locomotive,  it  makes  heat 
which  changes  water  into  steam,  and  the  steam  moves 
the  locomotive  and  cars.  This  is  one  of  the  ways  of 
making  use  of  the  energy  stored  in  coal.  If  the  coal 
were  burned  in  a  wrecked  locomotive  it  would  produce 
heat  just  the  same,  but  the  heat  would  be  wasted  as  far 
as  man's  immediate  use  is  concerned.  So  the  law  of 
the  conservation  of  energy  does  not  mean  that  energy 
cannot  be  wasted.  It  is  man's  business  to  use  his  energy 
and  all  kinds  of  energy  effectively  —  to  use  it  where  it 
will  bring  valuable  results. 

QUESTIONS  AND  EXERCISES 

1.  Examine    several   kinds  of  substances  and  note  any  differ- 
ences. 

2.  What  are  the  three  states  in  which  matter  can  exist? 

3.  Do  all  substances  in  the  liquid  state  have  the  same  tempera- 
ture? 

4.  In  which  of  the  three  states  are  the  following  most  useful: 
water,  iron,  silver,  mercury,  sugar,  gasoline,  coal? 

5.  What  holds  objects  on  the  earth? 


70  GENERAL  SCIENCE 

6.  What  makes  the  water  flow  in  creeks  and  rivers? 

7.  What  causes  wagons,  electric  cars,  and  sleds  to  run  down  hill 
easily? 

8.  Why  is  it  difficult  to  draw  a  heavy  wagon  up  a  hill? 

9.  As  far  as  you  know  from  experience,  does  the  law  of  the  con- 
servation of  energy  seem  to  be  true? 

10.  Which  requires  more  energy,  to  walk  on  the  level  or  up  a 
hill?    Why? 


CHAPTER  XI 
HEAT 

51.  Heat  is  a  form  of  energy  which  causes  all  molec- 
ular activity.  It  can  be  produced  by  the  chemical  action 
known  as  oxidation.  Since  energy  cannot  exist  apart 
from  matter,  heat  cannot  be  thought  of  except  as  a 
condition  of  matter.  The  faster  the  molecules  of  a  sub- 
stance move  the  more  heat  it  contains.  A  piece  of  iron 
which  is  red-hot  has  more  heat  in  it  than  when  it  can  be 
held  in  the  hand.  The  molecules  of  the  iron  are  also 
more  active  when  it  is  red-hot. 

Heat  is  made  in  our  homes  by  burning  wood,  gas,  or 
coal.  When  coal  is  burned  in  boilers,  the  heat  generated 
changes  water  into  steam.  When  gasoline  is  burned  in 
the  engine  of  an  automobile,  it  generates  enough  me- 
chanical energy  to  drive  the  machine  at  high  speed. 
Heat  generated  by  fires  is  used  to  melt  ores  and  for  the 
forging  of  iron.  Heat  is  used  to  prepare  our  meals, 
to  make  our  homes  comfortable.  It  enables  plants 
and  animals  to  grow  and  thus  produce  our  food.  By 
the  oxidation  of  the  food  in  our  bodies  we  are  kept 
warm  and  able  to  move  about.  All  of  us  have  daily 
experiences  with  heat  in  some  form.  Because  of  this 
close  relation  to  daily  life  it  is  important  that  every  one 
should  know  a  few  facts  and  laws  concerning  heat.  Every 
one  should  know  how  to  use  the  instruments  for  measur- 
ing the  degree  of  heat  of  a  body  and  something  about  the 
relative  amount  of  heat  that  given  substances  will  absorb. 


72  GENERAL  SCIENCE 

52.  Thermometers.  —  The  thermometer  is  an  instru- 
ment used  to  measure  the  degree  to  which  a  body  is 
heated,  that  is,  to  determine  its  temperature.     We  some- 
times use  our  fingers  or  even  our  whole  bodies  to  measure 
temperature.   We  often  put  a  finger  into  water  or  on  ob- 
jects to  see  if  they  are  hot  or  cold.     If  their  temperature 
is  higher  than  that  of  our  finger  we  say  they  are  hot. 
If  the  temperature  of  the  object  is  lower  than  that  of  our 
finger  we  say  it  is  cool  or  cold.     When  we  go  from  one 
room  to  another  we  say  that  the  rooms  are  of  the  same 
or   of    different   temperature,  according   to  our  feeling. 
Our  sensation  of  temperature  is  largely  determined  by 
the  condition  of  our  bodies  as  regards  health,  and  by  the 
moisture  conditions  of  the  surface  of  our  bodies  and  of 
the  air.     For  example,   70°  F.  in  January  would  be  a 
hot  day,  while  70°  F.  in  July  would  be  a  cool  day.     Moist 
air  in  winter  seems  cold  and  dry  air  seems  warmer.     In 
summer  dry  air  is  cool  and  moist  air  is  hot  to  our  feeling, 
while  the  actual  temperature  on  the  day  when  the  air 
is  moist  may  be  the  same  as  when  it  is  dry.     For  the 
above  reasons  our  bodies  do  not  make  very  good  ther- 
mometers.    Neither  can  we  determine  very  accurately 
the  temperature  of  water  or  any  object  with  our  fingers. 

Certain  substances  have  been  found  to  be  very  sensi- 
tive to  changes  of  temperature,  and  these  have  been  used 
to  construct  mechanical  thermometers,  of  which  there  are 
three  principal  types.  Only  two  will  be  considered  here. 
They  are  the  Fahrenheit  and  the  Centigrade  thermometers. 
The  Centigrade  thermometer  is  the  easier  of  the  two  to 
use,  as  its  scale  is  based  upon  the  decimal  system. 

53.  How  to  make   a   Thermometer.  —  Take   a   glass 
tube  about  1 2  inches  long,  with  a  very  fine  hole  at  one  end 
and  extending  through  to  a  closed  bulb  at  the  other  end. 


HEAT 


73 


Slowly  heat  it  to  a  very  high  temperature  to  drive  out 
all  moisture.  Slip  a  cork  tube  over  the  open  end  and 
have  the  cork  tube  tight  on  the  glass  and  extend- 
ing about  a  half  inch  above  the  end  of  the  glass 
tube.  Fasten  the  tube  securely  on  a  ring-stand 
in  a  vertical  position  and  fill  the  cork  cup  at 
the  top  almost  full  of  mercury.  Slowly  heat 
the  bulb  at  the  bottom  to  drive  out  some  of  the 
air  by  expansion.  After  a  few  air  bubbles 
escape  through  the  mercury,  allow  the  bulb  to 
cool  and  the  mercury  will  flow  down  as  the  air 
contracts  while  it  is  cooling.  After  the  mercury 
stops  flowing  down  heat  the  bulb  again  as  be- 
fore, and  then  let  it  cool.  Continue  this  process 

until  the  bulb  and  tube 
are  both  full  of  mer- 
cury and  all  the  air 
out. 

Take  the  thermo- 
meter tube,  now  full 
of  mercury,  and  slip  it 
through  one  of  the  two 
holes  of  a  rubber  stop- 
per and  put  it  into  a 
flask  containing  some  water. 
Do  not  let  the  bulb  touch  the 
water.  Put  a  tube  into  the 
other  hole  of  the  rubber  stopper 
to  direct  the  escaping  steam 
away  from  the  thermometer, 
and  heat  the  water  to  the  boil- 
ing point.  After  the  mercury  in  the  tube  ceases  to  flow 
out,  seal  the  top  by  directing  a  gas  flame  against  it  to 


THERMOM- 
ETER 
TUBE 


How  TO  LOCATE  THE  BOILING 
POINT 


74 


GENERAL  SCIENCE 


212< 


100° 


melt  the  glass,  but  at  the  same  time  keep  the  water 
boiling.  While  sealing  the  top  more  mercury  will  flow 
out  because  of  additional  expansion  due 
to  the  high  temperature  of  the  flame. 
As  the  glass  tube  cools  at  the  top  after 
having  been  sealed,  the  mercury  will 
contract  somewhat.  After  it  stops  con- 
tracting mark  the  top  of  the  mercury 
100°  for  the  Centigrade  thermometer 
or  212°  for  the  Fahrenheit. 

Remove  the  ther- 
mometer from  the 
flask  and  cool  it, 
and  then  place  it  in 
some  finely  cracked, 
melting  ice  from 
which  the  water  can 
escape.  After  the 
mercury  stops  con- 
tracting, mark  it  o° 
for  Centigrade  or  32°  for  Fahrenheit. 
This  will  be  the  freezing  point. 

To  make  a  Centigrade  thermom- 
eter,   divide   the    distance    between 
the  two  marks,  o°   and   100°,  into 
100  equal  parts.     To  make  a  Fah- 
renheit    thermometer,     divide     the 
space  between  32°  and  212°  into  180    PRINCIPAL    POINTS 
equal  parts.      Now  mark  off  spaces    THE     CENTIGRADE    AND 
below  32°  the  same   size   as   those 
above  it.    Do  the  same  on  the  Cen- 
tigrade scale.    Five-ninths  of  a  Centigrade  degree  is  equal 
to  one  degree  of  the  Fahrenheit  scale.     Why? 


How    TO    LOCATE 

THE  FREEZING 

POINT 


32 


40 


0° 


-17 


-40 c 


FAHRENHEIT    THERMOM- 
ETERS 


HEAT  75 

Mercury  freezes  at  40°  below  zero  and  boils  at  360° 
Centigrade  and  so  cannot  be  used  for  very  low  or  very 
high  temperatures.  Hydrogen  gas  thermometers  are 
used  for  extremely  low  and  high  temperatures. 

54.  Uses  of  Thermometers.  —  Thermometers  can,  of 
course,  be  used  only  to  determine  the  temperature 
of  a  substance.  To  determine  the  temperature  with 
a  mercury  thermometer  is  to  compare  the  molecular 
activity  of  a  substance  with  that  of  mercury.  When 
the  molecules  of  mercury  become  more  active  they 
need  more  room,  and  the  mercury  moves  up  the 
thermometer  tube.  The  amount  of  this  expansion  can 
be  read  by  the  degree  marks  on  the  tube.  The  tem- 
perature of  the  air  in  the  schoolroom  is  measured  by 
a  thermometer  on  the  wall.  What  kind  is  it?  What 
is  the  most  comfortable  temperature  of  the  air  for 
the  schoolroom  and  home?  Physicians  determine  the 
temperature  of  their  patients  by  placing  a  very  small 
thermometer  under  the  tongue  or  in  the  arm  pit.  The 
temperature  of  a  healthy  person's  body  is  about 
98.4°  F.  If  it  rises  very  much  above  or  falls  below 
the  normal  temperature,  there  is  something  physically 
wrong  with  the  individual. 

In  all  kinds  of  manufacturing  in  which  substances  are 
heated,  the  approximate  temperature  must  be  known, 
and  in  most  cases  the  exact  temperature  must  be  ascer- 
tained. The  temperature  of  the  ovens  for  baking  is 
carefully  watched;  also  the  temperature  of  the  sirup  in 
sugar  refineries;  and  especially  is  the  temperature  ob- 
served in  the  manufacture  of  fine  steel  for  razors  and 
watch  springs.  The  purity  of  substances  such  as  butter 
and  olive  oil  can  be  determined  by  noticing  their  char- 
acteristics at  a  given  temperature.  Pure  butter  will 


76  GENERAL  SCIENCE 

melt  at  about  94°  F.,  and  if  butter  does  not  melt  at  this 
temperature,  it  has  impurities  in  it. 

55.  Meaning  of  Temperature.  — Temperature  is  only 
the  degree  to  which  a  body  is  heated.  It  is  the  relative 
condition  of  a  body  with  respect  to  the  degree  of  heat 
of  other  bodies.  Suppose  that  a  pint  of  water  on  the 
stove  has  a  temperature  of  95°  C.  and  that  a  two  gallon 
bucket  full  has  a  temperature  of  95°  C.  Their  relative 
condition,  respecting  temperature,  is  the  same,  but  do 
they  have  the  same  amount  of  heat?  Which  quantity 
of  water  would  get  hot  quicker,  a  pint  or  two  gallons,  on 
the  same  fire?  Which  would  cool  quicker  after  being 
taken  off  the  fire?  Which  would  melt  the  most  ice  if 
slowly  poured  on  a  3oo-pound  block?  If  the  two  gal- 
lons of  water  on  the  same  fire  heat  more  slowly  than 
the  pint  of  water,  it  must  take  more  heat  to  raise  the 
temperature  of  the  two  gallons  to  95°  C.  than  it  does  to 
raise  the  pint  to  the  same  temperature.  If  the  two  gal- 
lons of  water  cool  more  slowly  than  the  pint  under  the 
same  conditions,  or  if  the  two  gallons  melt  more  ice  than 
the  pint  of  water,  then  the  two  gallons  must  have  had 
more  heat  than  the  pint  of  water  when  they  were  both  at 
the  temperature  of  95°  C. 

A  small  room  in  winter  can  be  heated  to  21°  C.  in  a 
short  time  with  a  small  fire,  but  to  heat  a  large  room  like 
an  auditorium  to  21°  C.,  in  winter,  would  require  several 
hours  with  a  large  fire.  Then  which  room  will  have  the 
more  heat  in  it  when  both  are  21°  C?  Which  one  will 
feel  the  warmer?  Which  will  take  longer  to  cool  if  only 
one  door  is  opened,  the  auditorium  or  the  small  room? 
Why? 

From  these  two  observations  it  can  easily  be  seen  that 
the  temperatures  of  the  two  quantities  of  water  and  the 


HEAT  77 

two  rooms  do  not  tell  you  how  much  heat  there  is  in  each, 
but  only  the  comparative  degree  of  heat.  The  tempera- 
ture does  help  in  finding  the  amount  of  heat  in  the  water. 
The  quantity  of  heat  put  into  a  gallon  of  water  cannot 
be  determined  unless  the  temperature  is  known  when 
the  heat  is  applied  and  also  when  the  water  is  removed 
from  the  fire.  But  a  degree  of  heat  on  the  thermometer  is 
not  a  unit  of  heat,  it  is  a  unit  of  temperature.  So  we 
need  to  make  use  of  another  unit,  the  unit  of  heat. 

56.  Calorie.  —  The  calorie  is  the  unit  of  heat.     The 
calorie  is  the  amount  of  heat  necessary  to  change  the  tempera- 
ture of  one  gram  of  water  i°  C.,  or  it  is  the  quantity  of 
heat  given  out  by  one  gram  of  water  when  it  cools  i°  C. 
If  500  grams  of  water  are  heated  from  5°  C.  to  25°  C.,  the 
change  in  temperature  is  20°  C.;    500X20  =  10,000,  the 
number  of  calories  of  heat  taken  up  by  the  water.     If 
1,000  grams  coolfrom  40°  to  25°,  the  amount  of  heat 
given  out  is  15X1000,  or  15,000  calories. 

To  measure  the  length  of  your  desk  you  would  use 
inches,  to  measure  the  length  of  the  room  you  would 
use  feet  or  yards,  to  measure  across  a  state  you  would  use 
miles.  All  are  units  of  length  but  of  different  size.  The 
reason  for  using  large  units  to  measure  large  quantities 
is  to  avoid  such  large  numbers.  So  for  measuring  a 
large  amount  of  heat  we  have  the  great  calorie  or  kilocalorie. 
It  is  1,000  times  as  large  as  the  calorie,  defined  above. 
The  great  calorie  is  used  in  measuring  the  heat  we  get 
from  foods  and  also  the  fuel  value  of  foods  for  animals. 
In  tables  giving  the  fuel  value  of  the  various  kinds  of 
foods,  the  calorie  used  is  the  great  calorie. 

57.  Specific  Heat.  —  Since  it  requires  more  heat  to 
change  the  temperature  of  a  gram  of  water  i°  C.  than 
to  make  the  same  change  in  the  same  weight  of  any 


78  GENERAL  SCIENCE 

other  substance,  except  hydrogen  gas  (which  is  not  con- 
venient to  work  with),  the  amount  of  heat  necessary  to 
change  the  temperature  of  i  gram  of  water  i°  C.  was  taken* 
as  the  unit  of  heat  —  the  calorie.  All  ordinary  substances 
require  less  than  a  calorie  of  heat  to  change  the  tempera- 
ture of  i  gram  i°  C.  If  a  pound  of  iron  and  a  pound  of 
water  (a  pint)  are  placed  on  a  hot  stove  or  a  gas  fire, 
which  will  get  too  hot  to  hold  in  the  hand,  the  quicker? 
The  temperature  of  the  iron  will  increase  about  nine 
times  as  fast  as  the  temperature  of  the  water.  The 
temperature  of  a  pound  of  mercury  will  increase  30  times 
as  fast  as  that  of  a  pound  of  water  under  the  same  condi- 
tions. That  is,  it  takes  30  times  as  much  heat  to  change 
the  temperature  of  one  gram  of  water  i°  C.  as  it  does  to 
change  the  temperature  of  one  gram  of  mercury  i°  C. 

Because  of  this  variation  in  the  amount  of  heat  neces- 
sary to  change  the  temperature  of  a  gram  of  any  substance 
i°  C.  we  have  what  is  called  specific  heat.  The  specific 
heat  of  a  substance  is  the  amount  of  heat  needed  to  change 
the  temperature  of  one  gram  of  that  substance  i°  C.,  or  it  is 
the  amount  of  heat  given  out  when  the  temperature  of 
one  gram  of  that  substance  falls  i°  C.  in  temperature. 
The  specific  heat  of  water  is  i,  of  iron  .11,  of  mercury 
.033,  of  copper  .095,  of  lead  .031.  That  is,  it  takes  .11 
of  a  calorie  to  change  the  temperature  of  i  gram  of  iron 
i°  C.,  and  .033  of  a  calorie  to  change  the  temperature  of 
i  gram  of  mercury  i°  C. 

58.  Sources  of  Heat.  —  The  chief  natural  source  of 
the  earth's  heat  is  the  sun.  The  rays  of  the  sun  warm 
the  surface  of  the  earth,  and  it  in  turn  warms  the  air. 
The  air  does  not  absorb  much  heat  directly  from  the 
sun's  rays.  It  is  the  sun's  heat  that  makes  our  summers 
warm  and  gives  energy  to  the  growing  vegetation  upon 


HEAT  79 

which  man  and  other  animals  are  dependent  for  food. 
Some  substances,  as  was  shown  in  §  55,  do  not  require  as 
much  heat  to  change  their  temperature  as  others.  It 
was  also  shown  that  water  per  unit  of  weight  requires 
more  heat  to  change  its  temperature  than  any  other  sub- 
stance except  hydrogen,  that  is,  its  specific  heat  is  greater 
than  that  of  any  other  substance.  So  when  in  the  sun- 
shine dry  ground  gets  warm  quicker  than  moist  earth, 
and  the  land  gets  warm  faster  than  the  water  of  lakes, 
rivers,  and  oceans.  For  this  reason,  land  surrounded 
by  water  or  near  a  body  of  water  does  not  become  very 
hot  in  summer,  and  is  not  so  cold  in  winter.  In  winter 
the  water  is  giving  out  the  great  quantity  of  heat  which 
it  absorbed  during  the  summer  and  thus  moderates  the 
climate  and  prevents  extreme  cold  weather.  For  this 
reason  it  is  possible  to  grow  large  quantities  of  fruit  along 
our  Great  Lakes. 

Other  sources  of  heat  are  the  chemical  processes  which 
man  employs  for  heat  production,  such  as  burning  wood, 
coal,  gas,  etc.  These  substances  all  contain  carbon, 
and  by  the  oxidation  of  carbon  much  heat  is  produced. 
The  heat  thus  produced  can  be  largely  regulated  by 
controlling  the  supply  of  fuel  and  the  rate  of  oxidation. 
Without  this  means  of  producing  heat  civilization  could 
not  exist.  Our  homes  'would  not  be  very  happy  places 
if  in  winter  we  had  to  eat  sufficient  food  and  wear 
enough  clothing  to  keep  our  bodies  warm  without  the 
aid  of  fire. 

59.  Effects  of  Heat.  —  In  the  chapter  on  Molecules 
and  Atoms1  we  learned  that  as  the  molecules  of  a  sub- 
stance become  more  active  they  require  more  space  and 
so  crowd  one  another  apart.  Heat  makes  the  molecules 

1   Chapter  III. 


8o 


GENERAL  SCIENCE 


more  active,  so  when  a  substance  is  heated  it  will  expand 
and  occupy  more  space  without  its  weight  being  increased. 
This  can  be  illustrated  by  taking  a  flask  completely  full 
of  water,  closing  it  with  a  rubber  stopper  having  a  glass 
tube  through  it,  and  heating  the  water.  As  the  water 
increases  in  temperature  it  will  expand  up  the  tube, 
(if  it  was  4°  C.  or  warmer  at  the 
start) .  If  a  substance  will  expand 
when  heat  is  added,  what  will  it 
do  when  heat  is  taken  from  it? 
Prove  your  answer  by  watching 
the  water  in  the  tube  as  the 
water  in  the  flask  cools. 

The  air  expands  when  heat  is 
applied  to  it.  This  can  be  proved 
by  taking  an  empty  flask  (but 
full  of  air)  and  closing  it  with  a 
cork  with  a  glass  tube  through  it. 
Hold  the  flask  in  both  hands  with 
the  end  of  the  tube  under  water. 
The  heat  of  the  hands  will  warm 
the  air  in  the  flask,  and  as  the  air 
expands  it  will  escape  from  the 
water  in  the  form  of  bubbles.  More  air  can  be  made  to 
escape  by  applying  a  Bunsen  flame  to  the  flask.  Remove 
the  heat  and  permit  the  flask  to  cool.  The  water  will 
now  flow  up  the  tube  into  the  flask,  because  the  air  in  the 
flask  contracts  as  it  loses  heat.  A  drop  of  ink  can  be 
made  to  flow  up  and  down  the  tube  by  alternately  heat- 
ing and  cooling  the  flask  a  few  degrees. 

A  brass  ball  which  will  just  slip  through  a  brass  ring 
when  both  are  at  ordinary  room  temperature  will  not 
pass  through  the  ring  when  it  is  heated.  If  the  ring  is 


SHOWING  How  WATER  EX- 
PANDS WHEN  IT  is  HEATED 


HEAT 


81 


EFFECT  OF  HEAT  ON  AIR 

As   the  air  is    heated    it   expands  and 
escapes  in  the  form  of  bubbles. 


heated  to  the  same  temperature  as  the  ball,  the  ball  will 
again  pass  through  it.  Why?  What  use  does  the  black- 
smith make  of  this  same 
principle? 

In  summer  the  tele- 
graph and  telephone 
wires  sag  because  of  in- 
crease in  length  due  to 
expansion.  In  winter 
they  contract  and  are 
then  stretched  tight  and 
produce  the  characteris- 
tic humming  noise  when 
the  wind  shakes  them. 
On  a  hot  summer  day 
the  concrete  walks  will 
sometimes  expand  so 
much  that  they  will  crack  or  crumble.  This  is  not 
usually  noticed  until  cold  weather  when  the  concrete  has 
contracted,  leaving  open  spaces  where 
it  broke  during  the  summer.  In  order 
to  avoid  much  of  the  breaking  of  walks 
by  the  action  of  heat,  expansion  creases 
are  put  in  about  every  three  or  four 
feet,  when  the  walk  is  laid.  The  cracks 
between  the  ends  of  railroad  rails  also 
provide  room  for  the  linear  expansion 
of  the  rails.  When  are  these  cracks 
HEAT  AND  METALS  between  the  railroad  rails  almost  closed 
and  when  are  they  open?  Why? 

Along  the  base  of  rock  cliffs  there  are 
quantities   of  small  stones   which   have 
fallen  from  above  because  they  were  moved  from  their 


When  the  brass 
ball  is  heated  it  will 
not  pass  through 
the  brass  ring. 


82  GENERAL  SCIENCE 

position  by  expansion  and  contraction  as  the  weather 
changed.  For  this  reason  it  is  often  dangerous  to  walk 
along  such  places.  Some  rock  may  lose  its  equilibrium 
at  any  time  and  plunge  to  the  bottom.  The  once  barren, 
rocky  plateaus  of  the  western  part  of  the  United  States 
have  been  so  changed  by  the  action  of  heat  and  water 
that  it  is  now  possible  to  cultivate  them. 

Water,  unlike  metals  and  rock,  expands  when  it  freezes 
and  so  assists  in  breaking  up  stones.  It  runs  into  the 
cracks  of  stones  and  freezes,  breaking  the  stones  apart 
and  shoving  the  outer  pieces  off  the  cliff.  It  runs  in  be- 
tween the  grains  of  a  rock,  and  when  it  freezes  it  causes 
the  rock  to  expand  so  much  that  the  rock  crumbles  and 
becomes  fine  earth  after  it  thaws  out  again.  In  this  way, 
in  the  temperate  climates,  the  stones  on  the  surface  are 
being  continually  broken  up.  Even  the  bricks  of  a 
house  are  made  to  crumble  by  the  freezing  of  the  water 
in  them.  Paint  will  keep  the  water  out  of  brick,  and  on 
this  account  it  is  used  as  a  preservative. 

In  general,  all  substances  —  solids,  liquids,  and  gases 
-  expand  when  heat  is  applied  to  them,  and  they  con- 
tract when  heat  is  allowed  to  pass  from  them.  Water, 
however,  is  an  exception  to  this  rule.  Water  is  most 
dense  at  4°  C.  That  is,  the  molecules  of  water  are  closer 
together  at  4°  C.  than  they  are  at  any  other  temperature, 
and  hence  a  gram  or  pound  of  water  will  occupy  less 
space  at  4°  C.  than  it  will  at  any  other  temperature. 
If  a  gallon  of  water  at  4°  C.  is  heated,  it  will  expand  and 
require  more  space.  If  it  is  cooled  below  4°  C.,  it  will 
expand.  When  water  freezes  it  expands  about  one- 
ninth.  Of  what  value  is  this  property  of  water  to  man 
and  to  the  animals  that  live  in  water? 


HEAT  83 

QUESTIONS  AND   EXERCISES 

1.  State  the  uses  made  of  heat  that  you  have  seen. 

2.  Does  your  body  serve  well  as  a  thermometer?     Why? 

3.  Why  does  the  mercury  of  a  thermometer  rise  in  the  tube  when 
the  air  around  it  becomes  warm? 

4.  What   temperature   on    the    Centigrade    thermometer   is   the 
same  as  32°  F?     98.4°  F?     °o  F?     70°  F?     -40°  F?     212°  F? 

5.  Where  do  you  have  your  thermometer  at  home?     Is  it  of 
more  use  outside  the  house  than  in  the  living  room?     Why? 

6.  Explain    the    difference    between    temperature    and    calorie. 
Give  the  use  of  each. 

7.  Name  the  different  ways  of  making  heat.     State  some  uses  of 
heat. 


CHAPTER  XII 
HEAT    OF   VAPORIZATION 

60.  When  water  in  a  vessel  is  placed  on  a  stove,  it  can 
be  made  to  escape  by  evaporation,  and  the  faster  heat  is 
applied  the  faster  it  evaporates.  The  temperature  of 
boiling  water  in  an  open  vessel  cannot  be  raised  above 
the  boiling  point.  The  escaping  steam  carries  the  heat 
away  as  fast  as  the  water  receives  it.  When  more  heat 
is  applied,  the  steam  escapes  faster  and  so  carries  off 
the  extra  amount  of  heat.  The  temperature  of  the 
steam  is  the  same  as  that  of  the  boiling  water,  but  a 
gram  of  steam  has  more  heat  in  it  than  a  gram  of  water 
has.  Since  the  temperature  of  the  boiling  water  cannot 
be  increased,  and  since  the  temperature  of  the  steam 
coming  from  the  boiling  water  is  the  same  as  the  tempera- 
ture of  the  water,  a  large  amount  of  heat  is  required  to 
change  the  water  from  a  liquid  into  a  gas  or  steam.  The 
number  of  calories  of  heat  required  to  change  one  gram  of  a 
boiling  liquid  into  steam  is  called  the  heat  of  vaporization 
of  that  liquid.  Since  it  takes  about  5!  times  as  long  com- 
pletely to  evaporate  an  open  vessel  of  water  as  to  raise 
it  from  o°  C.  to  100°  C.,  we  conclude  that  the  heat  of 
vaporization  of  water  at  100°  C.  is  about  533  calories. 
Accurate  experiments  show  that  the  heat  of  vaporiza- 
tion of  water  is  536  calories.  Other  liquids  have  a  dif- 
ferent number  of  calories  for  their  heat  of  vaporization. 
From  Chapter  X  we  learned  that  energy  cannot  be 
created  or  destroyed  but  can  be  transformed.  The 
large  amount  of  heat  required  to  change  water  into 


HEAT  OF  VAPORIZATION  85 

steam  must  be  in  the  steam.  This  heat  is  given  out 
again,  or  liberated,  when  the  steam  condenses  and  forms 
water.  The  heat  of  condensation  is  equal  to  the  heat  of 
vaporization.  This  can  be  proved  by  forcing  steam  into 
cold  water.  The  water  will  rapidly  increase  in  tempera- 
ture. This  is  also  illustrated  by  the  steam-heating 
system.  The  steam  comes  into  the  radiators  at  a  tem- 
perature of  about  1 00°  C.,  it  condenses,  and  the  water 
flows  out  at  about  the  same  temperature,  but  the  room 
containing  the  radiator  becomes  warm.  The  heat  comes 
from  the  steam  condensing  to  form  water. 

61.  Boiling  Temperature.  —  When  a  liquid  in  an  open 
vessel  is  heated,  it  will  be  found  that  there  is  a  certain 
temperature  above  which  it  cannot  be  raised,  no  matter 
how  fast  the  heat  is  applied.  At  this  temperature  bubbles 
of  steam  or  vapor  form  at  the  bottom  of  the  vessel  and 
rise  to  the  surface,  increasing  in  size  as  they  rise.  The 
temperature  at  which  this  occurs  is  called  the  boiling 
temperature  or  boiling  point.  Boiling  temperature  may 
also  be  denned  as  the  temperature  at  which  the  pressure 
of  the  steam  in  the  steam  bubbles  in  the  liquid  is  equal 
to  the  pressure  of  the  air  or  gas  on  the  surface  of  the 
liquid.  In  an  open  vessel  the  pressure  of  the  air  on  the 
liquid  determines  at  what  temperature  the  bubbles  of 
steam  will  form  in  the  liquid.  So  the  pressure  of  the  air 
determines  at  what  temperature  water  will  boil.  At 
"standard  pressure,"  which  is  about  average  air  pressure 
at  sea  level,  the  boiling  point  of  pure  water  is  100°  C. 
If  salt  or  sugar  is  dissolved  in  the  water,  it  will  not  boil 
until  it  is  heated  above  100°  C.,  depending  upon  the 
amount  of  salt  or  sugar  put  into  the  water.  Try  it. 

Water  on  the  top  of  a  mountain  will  boil  at  a  lower 
temperature    than    at    sea    level.     Why?     It    will    take 


86 


GENERAL  SCIENCE 


longer  to  cook  potatoes  on  top  of  Pikes  Peak  than  at 
Chicago.  Why?  In  the  city  of  Quito,  Ecuador,  water 
boils  at  90°  C.,  and  on  top  of  Mt.  Blanc  it  boils  at  84°  C. 
At  the  Dead  Sea  water  will  not  boil  until  its  tempera- 
ture is  over  100°  C.  In  a  steam  engine  in  which  the 
pressure  of  the  steam  is  100  pounds  per  square  inch  on 
the  surface  of  the  water,  the  boiling  point  is  155°  C. 

The  change  of  boiling  point  according  to  the  pressure 
on  the  water  can  be  illustrated  by  the  following  experi- 
ment. Take  a  flask  of  about 
400  cc.  capacity.  Fill  it  about 
half  full  of  water  and  heat  to 
the  boiling  point.  While  the 
water  is  still  boiling,  close  the 
flask  with  a  rubber  stopper, 
being  careful  to  remove  it 
from  the  fire  as  soon  as  closed. 
Invert  the  flask  on  a  ring- 
stand  and  pour  over  it  some 
cold  water.  The  cold  water 
cools  the  glass  and  causes  the 
steam  inside  to  condense.  This 
CHANGING  PRESSURE  condensation  reduces  the  pres- 

Showing  how  pressure  influences    sure  on  the  water  in  the  flask, 

boiling  point.  .     ,  ' 

and  the  steam  pressure  in  the 

water  becomes  equal  to  the  steam  pressure  on  the  water 
and  so  steam  bubbles  escape.  The  escaping  of  these 
bubbles  is  boiling.  This  cooling  of  the  flask  and  the 
boiling  of  the  water  in  it  can  be  continued  until  the 
water  can  be  made  to  boil  by  holding  the  flask  in  the 
hand.  The  author  has  made  water  boil  in  a  flask 
when  its  temperature  was  19°  C.,  by  placing  ice  on  top 
of  the  flask. 


HEAT  OF  VAPORIZATION  87 

Alcohol  boils  at  78°  C.,  ether  at  35°  C.,  liquid  air 
at  —  180°  C.,  and  liquid  carbon  dioxide,  at  —  80°  C.,  at 
standard  pressure. 

62.  Distillation.  —  Distillation  is  a  process  by  which 
liquids  are  separated  from  one  another  or  from  salts 
dissolved  in  them,  by  first  making  the  liquid  evaporate 
rapidly  by  the  application  of  heat  and  then  condensing 


DISTILLING  APPARATUS 


A,  is  the  boiler;    C,  the  condensing  tank;   D,  the  cold  water 
tank;   and  N,  the  distilled  water. 

the.  vapor.  The  condensed  steam  or  vapor  is  the  distilled 
product.  The  substance  to  be  distilled  is  placed  in  a 
closed  vessel,  A,  having  an  outlet  for  the  vapor  through 
a  tube,  B.  This  tube  passes  through  a  cooling  tank,  C, 
through  which  cold  water  is  kept  flowing.  As  the  vapor 
passes  through  the  coils  of  the  tube  in  the  cooling  tank, 
it  is  condensed  and  the  pure  liquid  flows  out  at  N. 


88  GENERAL  SCIENCE 

When  salts  or  other  substances  are  in  the  water,  the 
pure  water  can  be  separated  from  them  by  distillation, 
because  the  molecules  of  salt  are  too  heavy  to  escape 
from  the  liquid  with  the  vapor.  "Hard"  water,  there- 
fore, can  be  "softened"  by  distillation.  Water  for  the 
manufacture  of  ice  is  also  distilled.  Large  ocean  vessels 
get  pure  drinking  water  for  the  passengers  by  distilling 
the  salt  water  of  the  sea  instead  of  by  carrying  a  sufficient 
supply  of  drinking  water  from  the  port. 

The  commercial  uses  of  distillation  are  very  extensive. 
The  sap  of  the  long-leaf  pine  trees  is  collected  in  barrels 
and  taken  to  a  distillery  for  the  manufacture  of  turpentine 
and  rosin.  When  heat  is  applied  the  turpentine  evapo- 
rates rapidly  and  comes  out  as  the  distilled  product. 
The  rosin,  which  is  a  residue  of  distillation,  is  left  in  the 
boiler,  from  which  it  is  taken  for  the  market. 

In  Chapter  IV  we  learned  that  alcohol  is  a  waste  prod- 
uct of  the  yeast  plant.  Yeast  cannot  raise  the  quantity 
of  alcohol  in  a  liquid  to  more  than  14  per  cent.  In  order 
to  get  a  high  percentage  of  alcohol  the  process  of  distilla- 
tion is  used.  The  fermented  fruit  juices  or  fermented 
grains,  such  as  corn  or  rye  ground  up  and  mixed  with 
water  and  yeast,  are  distilled.  Since  pure  alcohol  boils 
at  78°  C.,  it  will  evaporate  much  faster  than  water  at 
78°  C.,  and  so  the  vapor  that  comes  from  the  fermented 
juices  may  contain  from  40  to  60  per  cent  of  alcohol, 
according  to  the  per  cent  of  alcohol  in  the  fermented 
juice.  This  distilled  product,  containing  from  40  to  60 
per  cent  of  alcohol,  can  be  distilled  again.  The  third 
time  that  it  is  distilled,  almost  pure  alcohol  is  obtained. 
To  this  distilled  product,  containing  80  to  90  per  cent 
of  alcohol,  quicklime  is  added.  The  lime  unites  with 
the  water  which  is  present  in  the  mixture,  but  it  does 


HEAT  OF  VAPORIZATION  89 

not  unite  with  the  alcohol.  The  alcohol  is  then  dis- 
tilled again  and  is  95  to  98  per  cent  pure,  and  this  is 
called  absolute  alcohol. 

Wood  alcohol  is  made  by  the  dry  distillation  of  wood. 
The  wood  is  placed  in  an  air-tight  retort  and  heated. 
Wood  alcohol  is  extremely  poisonous,  and  when  it  is 
burned  formaldehyde  is  produced,  which  is  very  hard  on 
the  eyes;  CHgOH  (Methyl  Alcohol)  +  O  (Oxygen)  = 
HCOH  (Formaldehyde)  +  H2O  (Water).  Some  labora- 
tory men  have  become  blind  by  continuous  use  of  wood 
alcohol  as  a  heat  producer. 

The  alcohols  which  are  made  by  the  yeast  plant  from 
grain  or  fruit  juice  and  purified  by  distillation  are  also 
poisonous,  but  not  so  much  so  as  wood  alcohol.  As 
beverages,  alcoholic  liquids  are  recognized  as  neither  neces- 
sary nor  desirable  for  the  best  of  health.  Many  well-known 
physicians  do  not  prescribe  them  for  medicines. 

Denatured  Alcohol  is  grain  alcohol  made  more  poison- 
ous by  adding  about  10  per  cent  of  wood  alcohol  or  other 
poisonous  liquid,  so  that  it  cannot  be  used  for  beverage 
purposes. 

63.  Fractional  Distillation  is  a  process  by  means  of 
which  mixed  substances,  each  having  a  different  boiling 
point,  are  separated  from  one  another.  This  is  done  by 
heating  the  mixture  to  the  boiling  point  of  each  substance 
in  succession  and  catching  the  condensed  vapor  in  sepa- 
rate vessels.  The  many  products  of  petroleum  are 
obtained  in  this  way.  Rhigolene,  which  boils  at  a  tem- 
perature of  between  20°  and  25°  C.,  is  the  first  to  vaporize 
and  pass  off.  This  is  followed  by  petroleum  ether,  boil- 
ing at  between  50°  and  60°  C.  Then  conies  gasoline, 
which  boils  at  70°  to  90°  C.;  then  naphtha,  boiling  at 
between  90°  and  120°  C.;  followed  by  benzine,  boiling  at 


90  GENERAL  SCIENCE 

between  110°  and  140°  C.,  and  kerosene,  which  boils  be- 
tween 150°  and  300°  C.  At  still  higher  temperatures  the 
heavy  lubricating  oils  pass  over,  and  lastly  vaseline  evap- 
orates. Of  the  residue  in  the  retort  paraffine  is  made. 

The  manufacture  of  alcohol  is  also  a  form  of  frac- 
tional distillation.  The  first  part  of  the  distillate  contains 
a  higher  percentage  of  alcohol  than  that  which  comes  off 
later. 

64.  Cooling  by  Evaporation.  —  We  have  learned  that 
when  water  in  an  open  vessel  is  boiling,  its  temperature 
cannot  be  raised  by  applying  more  heat,  because  the 
increased  heat  applied  is  carried  off  by  an  increase  in  the 
rate  of  evaporation.  That  is,  the  water  is  kept  cooled 
to  100°  C.,  by  evaporation.  To  cause  water  or  any 
other  liquid  to  evaporate  requires  heat.  Water  will 
evaporate  at  any  temperature,  but  most  rapidly  at  boil- 
ing point.  If  you  cover  your  hand  with  water  and  then 
swing  the  hand  it  soon  feels  cool  because  heat  is  taken 
from  the  hand  to  make  the  water  evaporate.  In  summer 
your  body  is  kept  cool  by  the  evaporation  of  the  sweat 
from  the  surface  of  the  body.  If  it  were  not  for  this 
natural  cooling  process  man  could  not  live  comfortably 
in  hot  climates.  Most  animals  are  kept  cool  in  the  same 
way.  The  evaporation  of  moisture  from  the  leaves  of 
plants  keeps  them  cool  and  prevents  the  hot  sun  from 
scorching  them.  A  heavy  rain  cools  the  ground  and 
streets  partially  by  evaporation.  In  cities  the  streets 
are  sometimes  sprinkled  to  cool  them.  Water  can  be 
made  to  freeze  in  summer  by  the  rapid  evaporation  of 
ammonia  or  ether.  When  liquid  carbon  dioxide  is 
allowed  to  escape  from  the  containing  cylinder,  it  evapo- 
rates so  rapidly  that  a  temperature  of  80°  C.  below  zero 
may  be  reached.  Mercury  can  easily  be  frozen  with  the 


HEAT  OF  VAPORIZATION  91 

frosty-looking   carbon   dioxide    which    comes    from    the 
cylinder. 

Butter  can  be  kept  cool  and  solid  by  keeping  moist 
cloths  around  it.  This  method  is  used  extensively  by 
good  housewives  in  the  country.  Cheese  and  other 
foods  can  be  kept  cool  in  the  same  way  with  little  expense 
and  labor.  Damp  clothing  should  never  be  worn,  be- 
cause heat  is  taken  from  the  body  in  order  to  evapo- 
rate the  moisture  in  the  clothing.  If  the  clothing  of  any 
particular  part  of  the  body  is  wet,  the  evaporation  may 
cool  the  body  so  much  that  the  person  will  catch  cold. 
Such  conditions  should  be  carefully  guarded  against. 

After  taking  a  bath  the  water  should  be  at  once  re- 
moved from  the  body  by  the  use  of  a  rough  towel  to 
prevent  the  loss  of  heat  by  evaporation  and  to  keep  up 
a  good  circulation  of  the  blood.  In  summer,  when  the 
air  has  about  all  the  water  vapor  that  it  can  hold,  the 
sweat  from  the  body  does  not  evaporate  fast  enough  to 
carry  off  the  excess  heat  and  so  we  become  uncomfort- 
ably warm  and  say  that  the  day  is  a  sultry  one.  The 
sultriness  is  due  to  the  lack  of  sufficient  cooling  by 
the  evaporation  of  sweat. 

QUESTIONS  AND   EXERCISES 

1.  Give  practical  uses  made  of  the  fact  that  vapors  carry  a  large 
amount  of  heat. 

2.  Does  water  boil  at  100°  C.  in  your  home?     In  your  school- 
room?    Why? 

3.  Name  all  of  the  distilled  products  that  you  have  seen.     State 
their  uses. 

4.  How  are  the  various  products  of  petroleum  obtained? 

5.  Does  evaporation  increase  or  decrease  the  temperature  of  the 
evaporating  substance?     What  practical  use  is  made  of  this? 


CHAPTER   XIII 
HEAT    OF   FUSION   AND    DISSOLUTION 

65.  If  water   is   placed   over  a   fire,   its   temperature 
slowly  rises  until  it  reaches  the  boiling  point.     The  heat 
then  applied  is  used  to  change  the  water  into  steam.     The 
temperature  of  the   steam  is  the  same  as  that  of  the 
water.     What  is  the  heat  required  to  change  water  into 
steam  called?     If  heat  is  taken  from  water  its  tempera- 
ture will  continue  to  decrease  until  it  reaches  the  freezing 
point.     Under   ordinary   conditions   the   temperature   of 
liquid  water  cannot  be  lowered  below  the  freezing  point, 
or  o°  C.     If  heat  is  taken  from  water  at  o°  C.  it  begins 
to  freeze  and  change  to  a  solid  form.     The  temperature 
of  the  ice  just  frozen  is  the  same  as  the  water  in  which 
it  is,  that  is,  o°  C.     A  relatively  large  amount  of  heat  is 
given  out  when  a  unit  mass  of  water  freezes. 

If  you  want  to  change  ice  into  water  a  relatively 
large  quant 'ty  of  heat  will  have  to  be  applied  just  to 
make  it  melt,  without  changing  its  temperature.  The 
temperature  of  the  melting  ice  cannot  be  changed.  It 
will  remain  o°  C.  until  all  is  melted.  All  the  heat  added 
is  used  to  change  it  from  a  solid  to  a  liquid  form.  The 
heat  required  to  melt  one  gram  of  ice  is  the  same  as  the 
amount  of  heat  given  out  when  one  gram  of  water  freezes. 
(What  law  does  this  suggest?) 

66.  Heat  of  Fusion.  —  The  heat  of  fusion  of  a  substance 
is  the  number  of  calories  of  heat  required  to  melt  one  gram 
of  that  substance  without  changing  its  temperature.     The 
amount  of  heat  required  to  melt  a  substance  is  the  same 


HEAT  OF  FUSION  AND  DISSOLUTION  93 

as  the  heat  given  out  when  that  substance  freezes.  So  the 
heat  of  fusion  is  the  same  as  the  heat  of  solidification.  The 
heat  of  fusion  of  ice  is  80  calories.  Every  time  one  gram 
of  water  at  o°  C.  freezes,  it  gives  out  80  calories  of  heat 
without  changing  its  temperature.  This  explains  why 
water  freezes  so  slowly  and  why  ice  melts  slowly.  After 
water  is  frozen,  the  tem- 
perature of  the  ice  will 
decrease  if  the  air  around 
it  is  below o°C.  The  spe- 
cific heat  of  ice  is  .5,  that 
is,  when  the  temperature 
of  one  gram  of  ice  is  low- 
ered i°  C.,  it  gives  out 
one-half  cal  rie  of  heat. 
Glass,  unlike  some 
other  substances,  does 
not  change  suddenly  into 
a  liquid.  After  it  begins 
to  melt  it  continues  to 

increase  in'  temperature 

.         111       ™i  BLOWING  GLASS 

if  heat  is   added.     The 

hotter  it  is  made  the  easier  it  will  flow.  This  is  important 
in  the  manufacture  of  window  panes,  as  it  permits  rolling 
the  glass  into  thin  sheets  when  in  a  semi-liquid  condition. 
67.  When  water  freezes  it  expands  about  one-ninth. 
Nine  gallons  of  water  when  frozen  will  become  ten  gallons 
of  ice.  The  weight  of  nine  gallons  of  water  is  the  same 
as  that  of  ten  gallons  of  ice.  Hence  nine  gallons  of  ice 
weigh  less  than  nine  gallons  of  water.  Why  does  ice  float 
on  water?  If  a  block  of  pure  ice  is  placed  in  water  what 
part  of  it  will  be  above  the  water?  Prove  your  answer 
by  placing  some  ice  in  water. 


94  GENERAL  SCIENCE 

Metals,  as  a  rule,  expand  when  they  change  from  a 
solid  to  the  liquid  form  and  contract  when  they  become 
a  solid.  Cast  iron  freezes  at  1200°  C.,  silver  at  954°  C., 
lead  at  330°  C.,  mercury  at  -  39.5°  C.  That  is,  these 
metals  become  solids  at  these  temperatures.  At  what 
temperature  do  these  same  substances  melt? 

68.  Effects  of  Salts  on  Freezing.  —  In  freezing  ice 
cream  salt  is  mixed  with  the  ice.  The  salt  melts  the  ice. 
It  requires  heat  to  melt  the  ice  and  to  dissolve  the  salt. 
The  heat  necessary  to  do  this  comes  from  the  cream,  and 
so  its  temperature  is  soon  lowered  to  the  freezing  point. 
The  application  of  ice  and  salt  is  continued  until  the 
cream  is  all  frozen.  When  water  has  as  much  common 
salt  dissolved  in  it  as  is  possible,  the  solution  will  not 
freeze  until  its  temperature  is  —  22°  C.  Why  does  ocean 
water  not  freeze  as  easily  as  river  water? 

If  equal  weights  of  ammonium  nitrate  (NH4N03)  and 
water  at  15°  C.  are  mixed,  the  temperature  will  decrease 
to  —  10°  C.  If  three  parts  of  calcium  chloride  (CaCy, 
in  crystal  form,  are  mixed  with  two  parts  of  snow,  a 
temperature  as  low  as  —  55°  C.  will  result.  This  mixture 
will  freeze  mercury.  These  two  salts  are  not  used  in 
making  ice  cream,  because  they  are  too  expensive. 

PROBLEMS 

1.  How  much  heat  is  required  to  change  the  temperature  of 
500  grams  of  ice  at  -20°  C.  to  o°  C?  (Specific  heat  of  ice  is  .5). 

2.  How  much  heat  is  required  to  change  500  grams  of  ice  at 
o°  C.  into  water  at  o°  C?  (Heat  of  fusion  of  ice  is  80  calories). 

3.  How  much  heat  is  required  to  change  500  grams  of  water 
at  o°  C.  into  steam  at  100°  C?  (Heat  of   vaporization  of  water 
is  536  calories). 

4.  How  much  heat  is  required  to  change  100  grams  of  ice  at 
-25°  C.  into  steam  at  100°  C? 

5.  If  an  iceberg  in  the  form. of  a  cube  is  40  feet  above  the  water, 
how  far  does  it  extend  down  into  the  water? 


CHAPTER  XIV 
HEATING   BUILDINGS 

69.  Transmission  of  Heat.  —  (a)  Radiation  is  the 
process  of  transferring  heat  in  straight  lines  through 
space  without  the  aid  of  ordinary  matter  or  material. 
All  of  us  have  had  the  common  experience  of  standing 
near  a  hot  stove  or  open  fire  in  a  grate,  or  near  a  steam 
or  hot  water  radiator,  and  receiving  the  heat  directly. 
If  we  stand  near  an  open  fire  in  a  cool  room,  the  part  of 
the  body  toward  the  fire  will  be  warm  while  the  opposite 
side  will  feel  cold.  If  two  persons  stand  near  an  open 
fire  one  behind  the  other,  the  one  in  front  next  to  the  fire 
will  receive  the  heat  while  the  one  behind  will  be  cold. 
If  an  object  is  placed  between  us  and  the  fire  or  radiator, 
the  object  reflects  and  absorbs  the  heat  and  we  do  not 
get  any.  If  we  stand  in  the  shade  of  a  tree  in  summer 
we  do  not  feel  the  hot  rays  of  the  sun.  All  of  these 
suggested  experiences  show  that  heat  radiated  from  a  hot 
object  travels  in  straight  lines,  and  many  good  authorities 
think  that  it  travels  as  fast  as  light,  namely  186,000  miles 
per  second.  The  heat  from  the  sun  comes  to  the  earth 
by  radiation.  Radiant  heat  passes  through  air  without 
heating  it,  so  the  upper  part  of  the  atmosphere  is  cold. 
The  lower  atmosphere  is  heated  by  the  air  coming  in  con- 
tact with  the  surface  of  the  earth  and  with  things  on  it. 
We  can  get  warm  standing  before  an  open  fire  even  if  the 
air  is  moving  past  us  toward  the  fire,  because  the  radiant 


96  GENERAL  SCIENCE 

heat  travels  with  such  great  speed  through  the  air  with- 
out heating  it. 

Glass  will  permit  radiant  heat  to  pass  through  it 
without  itself  being  heated.  For  this  reason  the  sun 
shining  through  the  windows  will  warm  a  room.  When 
the  sun  shines  on  a  greenhouse  the  heat  passes  through 
the  glass  and  makes  it  much  warmer  inside  than  the  air 
is  on  the  outside.  Not  much  of  the  heat  inside  the 
greenhouse  can  pass  out  by  radiation,  as  the  objects 
are  not  hot  enough  to  give  off  much  radiant  heat. 

(b)  Conduction  is  the  process  of  transferring  heat  in 
an  object  by  the  activity  of  the  molecules  in  the  object 
itself  or  by  two  objects  touching  each  other.  We  learned 
in  Chapter  XI  that  heat  is  a  form  of  molecular  activity. 
This  molecular  activity  can  be  transmitted  the  entire 
length  of  an  object  or  from  one  object  to  another  if  they 
are  in  contact.  We  have  experienced  the  results  of  con- 
duction by  placing  a  spoon,  knife,  or  fork  in  a  hot  sub- 
stance and  feeling  the  handle  become  warm ;  or  by  holding 
the  end  of  an  iron  poker  in  the  fire  until  the  end  in  the 
hand  became  almost  too  hot  to  hold.  How  does  the 
handle  of  a  smoothing  iron  get  hot?  Why  do  we  use  a 
cloth  on  the  handle  of  a  smoothing  iron? 

The  heat  from  the  fire  in  a  stove  passes  through  the 
stove  by  conduction  and  keeps  it  almost  as  hot  on  the 
outside  as  it  is  on  the  inside.  How  does  the  heat  pass 
from  the  stove  into  the  room?  The  hot  steam  in  a 
radiator  makes  the  iron  hot  and  the  heat  passes  through 
the  radiator  by  conduction,  but  it  passes  from  the  radia- 
tor into  the  room  by  radiation. 

Silver  is  the  best  conductor  of  heat  of  any  substance 
known.  Iron  conducts  heat  about  one-eighth  as  easily 
as  silver.  Glass  is  a  poor  conductor  of  heat,  only  about 


HEATING  BUILDINGS  97 

as  good  as  iron.  So  glass  prevents  the  escape  of  heat 
from  a  room  but  allows  the  radiant  heat  of  the  sun  to 
pass  through  it.  The  conductivity  of  water  is  only  about 
TfW  oi  that  of  silver. 

That  water  is  a  poor  conductor  of  heat  can  be  proved 
by  taking  a  tall,  narrow  vessel,  like  a  test  tube,  full  of 
water  and  making  the  water  on  top  boil  while  holding 
the  bottom  in  the  hand.  The  gas  flame  is  applied  only 
to  the  top  of  the  vessel. 
When  heat  is  applied  to  the 
bottom  of  a  vessel  of  water, 
the  water  on  the  top  is  heated 
by  a  process  different  from 
conduction.  Any  one  who 
has  been  in  bathing  in  a 
river  or  lake  knows  that  the 
water  is  warmer  on  the  top 
than  it  is  several  feet  below  BOILING  WATER 

the  surface.      Why?  IR  a  test  tube  while  holding  it  in 

.        J  the  hand. 

Gases  are  the  poorest  con- 


ductors known,  only  -^  as  good  as  water  or  -girrijTnr  as 
good  as  silver.  Air  is  a  gas,  and  because  gases  are  poor 
conductors  of  heat,  the  surface  of  the  earth  is  not  per- 
mitted to  cool  rapidly.  Gases  will  transmit  heat  easily 
when  they  are  free  to  move,  but  not  by  conduction. 

The  difference  in  the  rate  of  conductivity  can  be  ex- 
perienced by  placing  the  hand  on  a  piece  of  iron  and 
then  on  a  piece  of  dry  wood  lying  near.  The  iron  will 
feel  cooler  than  the  wood  in  winter  because  it  conducts 
the  heat  from  the  hand.  (For  this  reason  never  touch 
your  tongue  or  wet  ringer  to  a  piece  of  iron  during  zero 
weather).  The  iron  will  feel  warmer  if  both  iron  and 
wood  are  lying  in  hot  sunshine,  because  the  iron  will 


98  GENERAL  SCIENCE 

conduct  its  heat  to  the  hand.  The  difference  in  the  rate 
of  conductivity  of  substances  can  be  also  experienced  by 
stepping  with  bare  feet  from  a  woolen  carpet  on  to  an 
oilcloth  in  a  cool  room.  Linen  clothing  is  a  better  con- 
ductor of  heat  than  woolen.  At  what  time  of  the  year 
should  woolen  and  at  what  time  should  linen  be  worn? 
Why? 

The  influence  that  the  air  in  the  meshes  of  clothing 
has  upon  its  power  to  conduct  heat  is  very  great.  Felt, 
feathers,  and  fur  make  very  warm  coverings  because 
they  are  very  poor  conductors  of  heat  and  thus  prevent 
the  escape  of  heat  from  the  body.  Their  great  number  of 
minute  spaces  containing  air  or  other  gases  helps  to  make 
them  poor  conductors  of  heat.  Freshly  fallen  snow  is  a 
great  protection  to  such  crops  as  wheat,  rye,  and  hay. 

The  roots  of  fruit  trees  are 
also  protected  by  having  snow 
on  the  ground  during  very 
cold  weather,  as  the  ground 
does  not  freeze  very  deep 
under  the  snow. 

(c)  Convection  is  the  process 
of  transferring  heat  by  the 
flow  of  liquids  or  gases.  This 
process  can  be  illustrated  by 
placing  a  few  crystals  of  potas- 
sium permanganate  in  a  flask 

almost  full  of  clear  water  and 
CONVECTION  CURRENTS          then  glowly  heatjng  u  Qver  ft 

Showing  currents  while  water  is    -r>  -u  T«-U  i 

being  heated.  Bunsen  burner.     The  coloring 

matter  will  soon  reveal  currents 

of  water  moving  around  in  the  flask,  going  upward  just 
above  the  flame  and  downward  on  the  sides  of  the  flask. 


HEATING  BUILDINGS  99 

The  coloring  matter  will  be  uniformly  distributed  in  a 
very  short  time.  These  currents  distribute  the  heat  so 
thoroughly  that  the  water  in  all  parts  of  the  flask  is 
kept  at  about  the  same  temperature. 

The  water  nearest  the  flame  becomes  heated  and  ex- 
pands. It  is  thus  made  less  dense  than  the  surrounding 
water,  which  forces  the  less  dense  water  to  the  surface. 
While  on  the  surface  it  cools  a  fraction  of  a  degree  and 
becomes  more  dense  and  so  descends  at  the  edge  of  the 
flask  and  forces  the  slightly  warmer  water  up  from  the 
bottom.  It  can  easily  be  seen  how  this  method  differs 
from  conduction.  In  convection  the  whole  mass  of  mole- 
cules moves  and  warms  others  by  contact,  while  in  conduc- 
tion the  molecules  heat  their  neighbors  by  a  vibratory  motion. 

This  method  of  heat  transfer  is  illustrated  by  the 
heating  of  buildings  with  hot  air,  steam,  and  hot  water, 
and  even  to  some  extent  by  stoves  or  open  fires.  It  is 
also  illustrated  by  the  ocean  currents.  The  water  in 
and  near  the  Gulf  of  Mexico  is  heated  by  the  sun,  and 
this  warm  water,  the  Gulf  Stream,  moves  across  the 
Atlantic  Ocean  and  warms  the  whole  of  Western  Europe. 
The  Japan  Current  coming  across  the  Pacific  Ocean 
warms  our  Western  coast.  These  are  two  great  natural 
heating  plants.  The  convection  currents  of  the  ocean 
are  partly  caused  by  the  unequal  heating  of  the  water 
by  the  sun. 

Winds  are  also  partially  caused  by  unequal  heating  of 
the  earth's  surface,  and  therefore  they  are  convection 
currents  which  distribute  heat.  When  any  part  of  the 
earth's  surface  is  heated,  the  air  over  that  part  also 
becomes  heated  and  so  expands  and  becomes  less  dense, 
and  hence  it  is  not  so  heavy  as  the  cooler  air  surrounding 
this  heated  area.  This  cooler  air  is  soon  flowing  toward 


ioo  GENERAL  SCIENCE 

this  heated  area;  the  cool  air  moves  upward  as  fast 
as  it  is  heated,  thus  carrying  the  heat  away.  The 
movement  of  the  air  in  this  case  is  something  similar  to 
the  movement  of  the  water  in  the  flask  in  the  illustra- 
tion, but  on  a  much  larger  scale.  The  winds  and  ocean 
currents  are  the  great  natural  convection  currents  which 
distribute  heat  over  the  earth's  surface. 

70.  Primitive    Methods    of    Heating.  —  Man    in   his 
first  steps  toward  civilization  lived  much  like  some  of 
the  savages  to-day.     He  built  his  first  fires  out  in  the 
open  as  camp  fires  and  warmed  himself  by  them.     He 
then  built  the  same  kind  of  a  fire  inside  of  the  little  hut 
that  he  learned  to  make.      Over  this  fire  primitive  man 
also   cooked  his   food.     He   gradually  learned   to   build 
stones  around  the  fire  or  around  the  place  where  the 
fire  was  to  be  built.     Then  to  escape  the  evil  of  the 
smoke,  he  built  a  tall  top  to  his  stone  firebox.     This  top 
was  extended  until  it  carried  the  smoke  outside  his  little 
house.     This  stone  firebox  with  its  top  to  carry  away 
the  smoke  finally  developed  into  the  open  fireplace  and 
chimney,  such   as   the    early  settlers   used   in  America. 
This  type  of  open  fire  exists   now  in   the   form   of  the 
modern  grate    in  which  wood,    coal,  or   gas  is  burned. 
Metal  stoves  and  furnaces  are  modern  inventions  and  very 
convenient  in  comparison  with  the  ancient  methods. 

71.  Modern  Method  of  Heating.  —  Modern  man  tries 
to  have  the  smoke  and  gases  made  by  the  fires  carried 
from  his  home  without  poisoning  the  air  in  his  living 
rooms.     We  to-day  have  several  kinds  of  fuel  which  the 
ancients  did  not  have.     What  are  they? 

There    are    four   principal   modern    types    of   heating 
which  will  be  discussed  in  the  following  four  sections. 

72.  The    Open   Fire    and    Stove.  —  An   open   fire   of 


HEATING  BUILDINGS 


101 


wood,  coal,  or  gas  heats  the  room  by  radiation.  The 
floor,  walls,  and  objects  in  the  room  are  heated  directly 
by  radiation,  and  they  in  turn  warm  the  air  because  the 
air  comes  in  contact  with  them. 

When  stoves  are  used  all  three  methods  of  heat  transfer 
are  brought  into  action. 
The  fire  in  the  stove 
heats  the  iron.  This 
heat  is  carried  through 
the  iron  to  the  outside 
surface  by  conduction. 
A  large  part  of  the 
stove's  heat  passes  to 
the  objects  in  the  room 
by  radiation,  and  they 
in  turn  warm  the  air. 
Much  air  also  comes  in 
contact  with  the  hot 
stove  and  is  heated  by 

conduction.  After  it  is  heated  it  is  forced  upward 
rapidly  by  the  cooler  air  coming  toward  the  stove.  So 
there  is  a  continuous  current  of  air  rising  over  the  stove 
toward  the  ceiling.  It  flows  along  the  ceiling  to  the 
walls,  where  it  is  slightly  cooled,  and  descends  to  the 
floor  and  goes  to  the  stove  again. 

The  illustration  represents  the  heating  of  a  schoolroom 
by  the  use  of  a  stove.  The  fresh  air  from  the  outside 
goes  through  a  duct  to  the  base  of  the  stove,  where  it  is 
heated  and  forced  to  the  upper  parts  of  the  room  by 
the  inflowing  cold  air.  The  warm  air  gradually  cools 
and  drops  to  the  floor  and  moves  through  the  impure 
air  ducts.  By  this  method  the  greater  part  of  the  room 
is  heated  by  convection. 


CIRCULATION  or  AIR  WITH  A  STOVE 
IN  A  SMALL  ROOM 


102 


GENERAL   SCIENCE 


73.  Hot  Air  System.  —  The  hot  air  system  is  used 
extensively.  Many  public  institutions  use  it  by  having  a 
central  heating  plant  and  large  hot  air  ducts  leading  to 
the  various  buildings.  These  ducts  are  placed  under- 
ground and  the  air  is  forced  through  them  by  large  fans 


Vent  Flue 


Pure 


CIRCULATION  OF  AIR  IN  A  SCHOOLROOM 

The  foundation  enclosure,  F,  is  made  air-tight,  with  the  only  exit 
through  the  vent  flue,  N,  in  D.  The  enclosure,  E,  is  shut  off  from  F,  but 
communicates  with  the  outside  air  which  passes  through  the  register,  A, 
over  which  is  the  heater.  When  a  fire  is  started  in  the  heater,  the  air 
around  it  rises  and  the  outdoor  air  enters  through  E.  At  the  same  time 
the  heat  of  the  smoke  warms  the  air  in  the  vent  flue  through  the  partition, 
X,  and  creates  an  upward  draft  from  under  the  floor.  With  these  two 
drafts  there  is  a  continual  circulation  of  the  air  in  the  room  through  A 
and  the  small  registers,  R,  R,  R,  R,  and  up  the  vent  flue. 

run  by  engines  or  motors.  Fans  are  also  used  in  large 
buildings  where  there  is  only  one  heating  plant  in  the 
basement.  Small  private  houses  can  be  heated  by  this 
system  without  the  use  of  a  fan.  The  difference  in  the 
temperature  of  the  air  outside  and  that  at  the  furnace 
in  the  basement  is  sufficient  to  insure  the  flow  of  air  to 
the  various  rooms.  The  air  outside  the  house  is  cold 


HEATING  BUILDINGS 


103 


and  more  dense  than  the  hot  air  around  the  furnace,  so 

it  flows'  through  the 

cold,   fresh   air    duct 

to    the   furnace    and 

forces     the    hot    air 

through  the  hot  air  x 

ducts  to  the  rooms. 

The  air  keeps  flowing 

as   long   as   there  is 

a  fire  in  the  furnace, 

and  so  the  rooms  are 

kept  warm.    In  most 

private  houses  the  air 

coming  into  the  room 

from  the  furnace 

escapes  from  the 

room  through  the 

cracks  around  the 

windows   and  doors. 

This  method  provides 

for  ventilation. 

In  the  school  building  in  which  the  author  teaches, 

the  hot  air  system  of  heat- 
ing is  used.  The  fresh  air 
coming  from  the  outside 
passes  through  cloth  screens 
to  take  out  the  dust.  A 
large  fan  about  twelve  feet 
in  diameter  forces  the  air  to 
the  hot  furnaces  and  froni 
SHOWING  THE  MOVEMENT  OF  AIR  there  into  the  rooms  through 
IN  A  SCHOOLROOM  openings  near  the  ceiling  at 

one  corner.  The  rooms  are  warmed  by  convection  currents. 


Jr. 


HEATING  WITH  A  FURNACE  —  HOT  AIR 
SYSTEM 


104  GENERAL  SCIENCE 

At  the  floor,  just  under  the  place  where  the  hot  air  enters 
the  rooms,  is  another  opening  for  the  cool  and  impure 
air  to  leave.  It  goes  down  through  impure  air  ducts 
to  another  large  fan,  which  forces  it  to  the  outside  of  the 
building,  on  the  side  opposite  to  that  where  the  fresh  air 
enters.  The  illustration  shows  the  flow  of  air  in  one  of 
the  rooms.  The  air  comes  in  at  I  and  goes  out  at  0. 

74.  Steam  Heating  System.  —  The  steam  system  of 
heating  is  used  extensively  in  large  buildings  and  private 
houses.  The  apparatus  consists  of  a  steam  boiler  or 
boilers  in  the  basement.  The  size  and  number  of  boilers 
depend  upon  the  size  of  the  building  to  be  heated.  The 
radiators  in  the  rooms  and  halls  contain  a  heating  sur- 
face which  is  about  one  forty-fifth  of  the  numerical 
cubic  capacity  of  the  rooms.  The  steam  passes  from  the 
boilers  to  the  radiators  through  pipes,  and  the  condensed 
steam  or  water  flows  from  the  radiators  through  another 
set  of  pipes  which  lead  to  the  bottom  of  the  boilers. 

The  fire  in  the  boiler  changes  the  water  to  steam. 
The  pressure  of  the  steam,  which  is  never  more  than  a 
few  pounds  to  the  square  inch,  forces  the  steam  from 
the  boiler  through  the  pipes  to  the  radiators.  The  steam 
enters  the  radiators  at  a  temperature  of  about  100°  C. 
It  condenses  and  the  water  flows  from  the  radiator  at 
about  the  same  temperature.  If  this  is  true  how  does 
the  room  become  warm  from  the  radiator?  After  the 
steam  is  condensed  it  flows  back  to  the  boiler  to  be 
changed  into  steam  again.  So  the  water  keeps  up  a  con- 
tinuous motion,  flowing  from  the  boiler  to  the  radiators 
in  the  form  of  steam,  and  back  to  the  boiler  in  the  form 
of  liquid.  Is  this  conduction,  convection,  or  radiation? 

The  flow  of  steam  into  the  radiator  is  controlled  by  two 
valves  on  the  radiator:  one  large  valve  lets  the  steam 


HEATING  BUILDINGS 


105 


into  the  radiator  and  also  lets  the  condensed  steam  or 
water  out  of  the  radiator.  Somewhere  on  the  radiator, 
toward  the  opposite  side  or  end  from  the  large  inlet  valve, 
is  a  small  valve 
which  permits  the 
air  to  escape  when 
the  steam  is  turned 
on  and  also  lets  in 
air  so  that  the 
water  can  flow  out 
of  the  radiator 
when  there  is  no 
steam  in  the  boiler. 
The  small  valve,  if 
in  good  condition, 
closes  automati- 
cally as  soon  as  all 
the  air  is  out  of  the 
radiator  and  the 
hot  steam  begins 
to  escape.  The 
valve  opens  again 
after  it  cools. 

In  this  system  the  heat  is  carried  from  the  boiler  to 
the  radiator  by  convection.  The  radiator  is  heated 
on  the  inside  by  conduction.  The  heat  passes  through 
the  radiator  by  conduction.  The  heat  passes  into  the 
room  partly  by  radiation  and  partly  by  conduction. 
The  air  which  touches  the  radiator  is  heated  by  con- 
duction and  so  becomes  less  dense  and  is  forced  toward 
the  ceiling  by  the  cooler  air  moving  toward  the  radiator. 
This  process  causes  convection  currents  to  be  set  up  in 
the  room  and  so  the  whole  room  is  heated. 


STEAM-HEATING  SYSTEM 


io6 


GENERAL   SCIENCE 


When  the  radiator  is  in  the  room,  no  provision  is 
usually  made  by  the  heating  system  for  ventilation  as 
in  the  hot  air  system.  The  rooms  have  to  be  ventilated 
by  opening  the  windows  or  by  air  ducts  which  permit  air 
to  enter  under  the  radiators. 

What  is  known  as  the  hot  air  and  steam  system  com- 
bined is  sometimes  used  in  large  buildings.  In  this 
combination  the  steam  radiators  are  placed  in  the  base- 
ment and  the  cool,  fresh  air  is  forced  over  them  and 
into  the  rooms  by  large  fans  and  the  impure  air  removed 
from  the  rooms  by  a  fan,  as  in  the  hot  air  system.  This 
is  sometimes  called  the  indirect  system  of  heating. 

75.  Hot  Water  System. -- The  hot  water  system  is 
very  similar  to  the  steam  system  except  that  the  boiler 
in  the  basement  and  the  radiators  in  the  rooms  and 

the  pipes  leading  to  them 
are  all  full  of  water,  and  a 
pipe  extends  to  an  expan- 
sion tank  in  the  upper  part 
of  the  house.  This  tank 
receives  the  overflow  of 
water  due  to  expansion  by 
heating.  There  are  pipes 
leading  from  the  boiler  in 
the  basement  to  the  radia- 
tors, and  a  system  of  pipes 
leading  from  the  radiators 
in  the  rooms  to  the  bottom 
of  the  boiler  in  the  basement,  and  through  these  the 
water  flows  from  the  radiators  after  it  has  cooled. 
In  this  system  of  heating  all  three  methods  of  transfer 
of  heat  are  used.  The  heat  from  the  fire  in  the  boiler 
is  carried  through  the  metal  of  the  boiler  by  con- 


HOT  WATER  HEATING  SYSTEM 


HEATING  BUILDINGS 


107 


duction  and  transmitted  to  the  water  in  the  boiler  by 
conduction.  The  water  next  to  the  hot  iron  in  the  boiler, 
as  it  receives  the  heat  expands,  that  is,  becomes  less 
dense,  and  is  then  forced  upward  by  the  cooler  water  at 
the  bottom  of  the  boiler,  which  is  more  dense.  The 
supply  of  cool  water  is  kept  constant  by  the  return  from 
the  radiators  in  the  rooms. 

This  hot  water  is  thus  forced  through  the  pipes  from 
the  boiler  to  the  radiators  and  transmits  its  heat  to  the 
metal  of  the  radiators  by  conduc- 
tion. The  heat  passes  off  the  ra- 
diator into  the  room  partly  by 
radiation,  warming  the  objects  in 
the  room,  and  partly  by  conduction 
to  the  air  which  is  touching  the  ra- 
diator. This  air,  as  it  is  warmed, 
is  forced  toward  the  ceiling  by  the 
cooler  air  in  the  room  flowing 
toward  the  radiator,  where  it  in 
turn  is  heated  and  forced  toward 
the  ceiling;  thus  convection  cur- 
rents are  set  up  in  the  air,  which 
distribute  the  heat  of  the  radiator 
to  all  parts  of  the  room.  The  heat 
is  transmitted  from  the  boiler  to 
the  radiators  in  the  rooms  by  the 
flow  of  the_  water.  What  method 
of  transferring  heat  is  this? 

The  hot  water  system  of  heating  is  one  of  the  most 
economical  that  can  be  used  in  a  private  house.  By 
this  system  the  temperature  of  the  house  can  be  most 
easily  controlled  in  the  early  fall  and  late  spring.  A 
small  fire  in  the  boiler  will  warm,  the  water  sufficiently 


STEWART  HEATER  FOR 
HOT  WATER  SYSTEM 


io8 


GENERAL  SCIENCE 


in  the  early  fall,  when  not  much  heat  is  needed  in  the 
rooms,  to  cause  the  water  to  flow  from  the  boiler  to  the 
radiators.  The  water  thus  flowing  through  the  radiators 
is  not  very  hot  and  will  not  give  to  the  rooms  an  excess 
of  heat  like  steam  radiators.  For  example,  the  water 
in  the  radiator  may  be  at  a  temperature 
of  only  140°  F.,  and  therefore  not  much 
heat  will  pass  into  the  room,  while  in 
the  steam  system  the  radiator  with  steam 
in  it  has  a  temperature  of  212°  F.,  and 
hence  will  give  off  to  the  air  in  the  room 
much  more  heat  than  is  usually  wanted. 
The  expansion  tank  in  the  upper  part 
of  the  house  is  usually  kept  about  half 
full  of  water.  As  the  boiler  and  all  the 
water  pipes  and  radiators  must  be  kept 
completely  full  of  water,  the  water  will 
have  to  have  some  open  vessel  into 
which  the  extra  volume  due  to  expansion 
by  heating  can  flow,  or  else  the  radiators 
or  pipes  or  boiler  would  burst  when  the 
water  is  heated.  The  expansion  tank 
is  usually  connected  with  the  outside 
of  the  house  by  an  open  pipe  leading  to 
a  sink  or  to  the  roof.  Through  this  pipe 
the  water  can  flow  if  the  expansion  tank 
is  too  small  to  hold  the  extra  volume  of 
WATER  SYSTEM  or  water  jue  to  expansion  by  heating. 

HEATING  .  . 

During   extremely   cold    weather   the 

boiler  and  the  water  pipes  in  the  hot  water  system  must 
be  drained  if  no  fire  is  kept  in  the  boiler,  in  order  to  pre- 
vent the  bursting  of  the  pipes  by  freezing. 

76.   Fireless  Cooker.  —  A  fireless  cooker  may  be  made 


APPARATUS  ILLUS- 
TRATING THE  HOT 


HEATING  BUILDINGS 


109 


by  taking  a  large  box  and  putting  into  it  about  6  inches 
of  hay  or  sawdust  or  cork  shavings  and  on  top  of  this 
material  setting  another  box  of  wood  or  paper  of  such  a 
size  that  a  space  of  about  6  inches  will  be  left  between 
the  sides  of  the  two  boxes  and  also  about  4  inches  from  the 
top  of  the  inside  box  to  the  top  of  the  outside  box.  The 
space  between  the  two  boxes  should  be  filled  with  the 
same  kind  of  packing  material  that  was  used  in  the 
bottom.  The  lid  should  fit  the  top  of  the  large  box  and 
be  about  4  inches  thick  with  packing  material  between  the 
upper  and  lower  surfaces  of  the  lid.  When  the  vessel  of 
boiling  hot  food  is  placed  in 
the  box  and  the  lid  closed, 
the  heat  cannot  escape;  the 
food  to  be  cooked  is  thus 
kept  at  almost  the  same 
temperature  as  when  it  was 
placed  in  the  fireless  cooker. 
Hence,  the  food  will  cook  the 
same  as  if  left  on  the  fire, 
but  a  little  more  slowly,  be- 
cause a  small  amount  of  heat 
will  escape  from  the  food 
to  warm  the  inside  of  the 
fireless  cooker. 

The  two  walls  of  the  fireless  cooker,  with  the  packing 
of  sawdust  or  cork  shavings  between,  enclose  a  great 
amount  of  air  in  the  little  spaces  between  the  packing. 
Air,  being  a  gas,  is  a  very  poor  conductor  of  heat,  and  the 
packing  prevents  convection  currents  from  being  formed, 
and  so  the  heat  cannot  pass  from  the  inside  of  the  cooker 
to  the  outside;  thus  the  material  is  kept  at  the  same 
temperature  as  when  it  was  placed  in  the  cooker. 


FIRELESS  COOKER 

Made  of  two  boxes  and  cork 

packing. 


no  GENERAL  SCIENCE 

It  is  not  necessary  to  go  to  any  great  expense  to  enjoy 
the  use  and  advantages  of   a  fireless   cooker.     All  you 
need  to  do  is  to  get  two  store  boxes  of  proper  size  and 
some  packing  material  to  be  placed  between  the  two  as 
described  above.     Any  family  desiring  the  use  of  a  fire- 
less  cooker  can  easily  make  one  and  enjoy  the 
I   I         increased  flavor  of  their  food  cooked  in  such 
'(      i\      a  manner. 

The  "thermos  bottle"  is  a  modified  form  of 
the  fireless  cooker.     It  is  made  of  two   glass 
bottles,  one  sealed  inside  of  the  other  at  the 
neck  in  such  a  way  that  air  cannot  pass  in  or 
out  between  the  two  bottles.     Just  before  seal- 
ing the  inside  bottle  to  the  outside  one,  the  air 
CROSS        between  the  bottles  is  pumped  out,  thus  leav- 
SECTION  OF    ing  nothing  between  the  two  bottles  which  can 
THERMOS     transmit  heat  from  the  inside  bottle  to  the  out- 
side one  by  convection  or  conduction.    The  out- 

riafiifthe  In-  side  bottle  is  lmed  on  tne  inside  by  a  bright, 
side  bottle,  reflecting  metal  which  prevents  the  escape  of 
side  bottle,  any  heat  from  the  inside  bottle  by  radiation. 

QUESTIONS   AND   EXERCISES 

1.  Why  do  gardeners  make  hotbeds  with  glass  tops? 

2.  Why  does  an  iron  handle  of  a  cooking  utensil  get  so  much 
hotter  than  a  wooden  handle? 

3.  What  advantage  is  it  to  birds  to  have  their  feathers  standing 
out  straight  from  their  bodies  in  winter  instead  of  lying  down  smooth 
as  in  summer? 

4.  Why  do  animals  living  in  cold  regions  have  a  heavy  coat  of 
fur? 

5.  How  does  clothing  keep  you  warm  in  winter?     In  summer? 

6.  Why  are  cold  storage  rooms  built  with  a  double  wall  and  the 
space  between  filled  with  sawdust  or  other  material? 

7.  Why  will  ice  packed  in  sawdust  not  melt? 


HEATING   BUILDINGS  in 

8.  Examine  your  heating  system.     What  kind  is  it?     How  does 
the  heat  of  the  fire  get  to  the  air  in  the  rooms? 

9.  Light  a  candle  and  take -it  to  different  parts  of  the  room  and 
note  which  way  the  air  is  moving.     Make  a  drawing  to  show  the 
circulation  of  the  air. 

10.  Steam  comes  into  the  steam  radiators  at  a  temperature  of 
100°  C.  and  the  water  of  the  condensed  steam  flows  from  the  radiator 
at  about  the  same  temperature;    where  does  the  heat  that  warms 
the  room  come  from? 

11.  How  much  heat  will  the  air  in  a  room  receive  from  a  radiator 
in  12  hours  if  10,000  grams  of  steam  at  a  temperature  of  100°  C. 
come  into   the  radiator  each  hour,  and  if  water  flows  out  of  the 
radiator  at  a  temperature  of  95°  C? 

12.  If  boiling-hot  food  is   placed   in  a   fireless   cooker,  will   the 
temperature  of  the  food  increase  or  decrease?     Why?     Will  it  cook? 
Why?    Why  will  the  flavor  of  food  thus  cooked  be  increased? 


CHAPTER   XV 
FOOD 

77.  The  Human  Body  a  Machine.  —  The  human  body 
has  certain  characteristics  similar  to  those  of  a  locomotive 
or  engine.  It  needs  fuel  from  which  to  obtain  energy 
for  movement.  This  fuel  must  be  oxidized  to  produce 
heat,  which  is  transformed  into  muscular  energy  and 
enables  the  body  to  move  about  as  the  individual  desires. 
The  locomotive  has  in  it  fire  from  which  the  heat  is 
transmitted  to  the  water  in  the  boiler.  The  water  is 
changed  into  steam,  the  steam  under  the  control  of  the 
engineer  is  allowed  to  pass  to  the  cylinders  and  drives  the 
piston  back  and  forth  by  the  energy  which  it  received 
from  the  fire,  and  thus  the  heat  energy  of  the  steam  is 
transformed  into  mechanical  energy.  The  wheels  of 
the  locomotive  are  made  to  turn  and  the  whole  machine 
moves  along  the  track. 

The  engineer  in  the  cab  of  the  locomotive  corresponds 
to  the  brain  in  the  human  body.  The  engineer  controls 
the  locomotive  by  controlling  the  steam.  The  brain 
controls  the  energy  in  the  human  body  by  controlling 
the  production  of  heat  energy,  its  use,  and  its  escape 
from  the  body.  The  locomotive,  however,  must  have 
persons  in  charge  of  it  and  a  continual  supply  of  fuel  to 
make  it  a  machine  by  which  work  can  be  done.  The 
human  body  needs  a  continuous  supply  of  fuel,  which  is 
taken  in  the  form  commonly  called  food,  but  it  does  not 


FOOD  113 

need  an  engineer  or  fireman.  It  is  a  self -con  trolling 
machine  and  is  also  able  to  obtain  the  fuel  necessary 
to  keep  it  in  an  active  state. 

78.  Cells.  —  The  whole  human  body  may  be  thought 
of  as  a  living  organism  which  is  made  up  of  parts  called 
organs,  such  as  the  heart,  the  lungs,  the  hands,  etc. 
Each  organ  is  made  up  of  several  tissues.  For  example, 
the  heart  is  composed  of  muscular 
tissue,  nervous  tissue,  connective 
tissue,  and  a  few  others.  Each 
tissue  is  made  up  of  smaller  parts 
called  cells.  A  cell  is  the  smallest 
division  of  a  living  body  which  can 
do  the  things  necessary  to  sustain  its 

life  and  that  of  the  body  of  which  the  FLAT  C™™  THE 
cell  is  a  part.  The  cells  can  take 
in  food,  can  breathe,  can  throw  off  waste  matter  such  as 
carbon  dioxide  and  nitrogen  compounds,  and  can  grow 
and  make  other  cells.  These  are  called  the  functions 
of  life. 

In  order  that  cells  may  carry  on  such  activities,  it  is 
necessary  for  them  to  have  a  continuous  supply  of  food, 
and  the  more  active  they  are  —  as  when  a  person  is  at 
work  —  the  more  food  they  need.  There  is  no  time  when 
all  the  cells  of  the  body  are  at  rest,  and  on  this  account 
it  is  necessary  to  take  food  even  when  we  are  not  at  con- 
tinuous or  regular  work.  The  cells  in  the  human  body 
keep  up  a  continuous  work  of  reconstruction  and  growth 
in  order  that  the  whole  body  may  be  in  the  best  possible 
condition  of  health.  When  not  enough  exercise  is  taken 
to  cause  the  waste  matter  of  the  cells  to  be  carried  away 
as  fast  as  it  is  produced,  and  to  cause  a  fresh  supply  of 
food  to  be  carried  to  the  cells,  then  the  cells  are  not  able 


ii4  GENERAL  SCIENCE 

to  do  their  best  work  and  the  whole  body  may  begin  to 
feel  the  results  coming  from  the  reduced  activity  of  the 
cells.  This  condition  of  the  body  is  usually  known  as 
sickness. 

The  cells  of  the  body  are  very  active;  some  organs 
never  cease  their  activity  except  for  fractions  of  a  second; 
and  new  cells  are  continually  being  made  in  the  body 
to  replace  the  old  ones  which  have  been  used  up  or  oxi- 
dized. For  these  reasons  a  sufficient  amount  of  food  must 
be  taken  into  the  body  to  supply  the  fuel  and  the  building 
material  necessary  to  keep  up  all  these  vital  activities. 
There  are  some  foods  which  we  eat  that  are  used  only  for 
the  production  of  heat,  thus  enabling  the  body  to  move 
about  freely.  There  are  other  foods  which  are  used  for 
the  repair  of  old  cells  that  have  been  torn  down  and  for 
building  up  new  ones  when  the  body  is  growing.  All 
the  foods  that  we  eat  may  be  divided  into  two  classes, 
which  are  (i)  nutrients  and  (2)  inorganic  foods  like  water 
and  salt. 

79.  Nutrients. -- The  three  nutrients  are  carbohy- 
drates, fats,  and  proteids  or  protein.  These  are  also 
called  organic  foods  or  organized  foods.  They  all  come 
from  plants  and  animals.  Since  the  body  needs  food 
both  for  the  production  of  heat  and  for  building  material, 
it  is  necessary  that  we  eat  some  foods  which  are  easily 
oxidized  and  produce  much  heat,  and  also  eat  foods 
which  are  easily  transformed  into  flesh  and  bone,  so  that 
the  body  may  retain  its  weight.  The  body  also  will  be 
kept  more  healthy  if  just  a  sufficient  amount  of  each  class 
of  food  is  eaten  to  produce  the  proper  amount  of  fuel 
and  building  material.  In  order  to  understand  which 
foods  are  for  fuel  and  which  build  cells,  it  will  be  neces- 
sary to  study  the  three  nutrients  carefully. 


FOOD  115 

(a)  Carbohydrates.  —  Carbohydrates  are  so  called  be- 
cause they  contain  hydrogen  and  oxygen  in  the  same 
ratio  as  water,  that  is  2  to  i.  Carbohydrates  are  com- 
posed of  carbon,  hydrogen,  and  oxygen.  The  pure  forms 
of  carbohydrates  are  sugar  and  starch.  The  chemical 
composition  of  starch  is  CeHioOs,  and  that  of  grape  sugar 
is  C6Hi2O6.  From  these  compounds  you  can  see  that 


SUGAR  FACTORY 

the  hydrogen  and  oxygen  are  in  the  same  ratio  as  in  water, 
that  is,  2  to  i.  The  carbohydrates  are  digested  in  the 
mouth,  in  the  stomach,  and  in  the  intestines,  and  are  then 
carried  by  the  blood  to  the  liver,  where  they  are  stored, 
and  given  out  and  carried  to  all  parts  of  the  body  as 
they  are  needed.  A  part  of  the  carbohydrates  is  oxidized 
in  the  liver  to  make  heat  and  the  rest  is  oxidized  in  the 
blood  and  in  the  muscle.  The  part  oxidized  in  the 
muscle  produces  energy  which  enables  the  body  to  move. 
Carbohydrates  are  also  sometimes  stored  in  the  body 
in  the  form  of  fat;  that  is,  fat  is  made  out  of  the  carbo- 


n6 


GENERAL  SCIENCE 


hydrates  by  the  body.  Not  very  much  food  can  be  stored 
in  the  liver  or  in  the  muscle  in  the  form  of  carbohydrates, 
and  so  a  continuous  supply  of  food  must  be  going  from 
the  digestive  organs  to  the  liver  and  the  other  parts  of 
the  body.  In  order  to  keep  up  this  supply,  food  must 

be  eaten  every  few  hours, 
especially  during  the  time  when 
we  are  awake  and  are  working 
hard. 

Foods  which  contain  carbo- 
hydrates are  those  made  of 
corn,  wheat,  oats,  barley,  etc. 
Apples,  oranges,  grapes,  plums, 
peaches,  and  pears  have  carbo- 
hydrates, mostly  in  the  form  of 
sugar.  Bananas  when  thorough- 
ly ripe  have  both  starch  and 
sugar,  and  should  not  be  eaten  except  when  they  are 
ripe.  Bananas  which  have  a  green  appearance  are  nearly 
all  starch,  and  the  starch  is  in  such  a  condition  that 
it  is  very  hard  to  digest.  Bananas  in  that  state  of  ripe- 
ness should  never  be  eaten.  The  starch  in  green  bananas 
is  about  the  same  as  the  starch  in  raw  potatoes  and  has 
nearly  the  same  taste;  both  are  very  hard  to  digest. 
When  the  banana  ripens  the  starch  is  changed  to  sugar, 
and  when  the  potato  is  cooked  the  starch  is  acted  upon 
by  the  heat  and  made  easy  to  digest. 

(b)  Fats.  —  Fats  are  substances  such  as  butter,  lard, 
and  tallow  from  animals,  and  olive  oil,  cotton  seed  oil, 
and  linseed  oil  taken  from  plants.  All  the  cereals  like 
those  which  are  made  from  corn,  wheat,  and  oats  have 
fat  in  them.  Fat,  being  unlike  sugar  in  composition, 
will  not  dissolve  in  water.  Fats  can  be  made  to  mix 


LIVER  CELLS 
Where  the  glycogen  is  stored. 


FOOD  117 

with  water  by  using  a  chemical  base.  Olive  oil  can  be 
made  to  mix  with  water  if  a  small  quantity  of  ammonia 
or  potassium  hydroxide  is  added.  When  oils  are  mixed 
with  water  by  the  aid  of  a  base  the  mixture  is  known  as 
an  emulsion.  The  most  perfect  emulsion,  in  which  no 
base  is  used,  is  milk.  Hot  soups  have  more  or  less  fat 
mixed  with  the  water  and  are  very  poor  emulsions. 

Fats,  like   carbohydrates,    are   composed  of   hydrogen, 
carbon,  and  oxygen,  but  they  do  not  have  very  much  oxy- 
gen, and  therefore  a  great  quantity  of  oxygen  is  required 
to  oxidize  them.     Since  much          ^>0  o^^     /~\oc> 
oxygen  is  used  in  the  oxida-      °  °  0  °  OQ  *     ^MP   0° 
tion    of    fats,    they    produce   °  °  °  £>gofQ   °o  0*0  ° 
about  two  and  one-fourth  times        o°«»o00J0OoO 
as    much    heat    as    carbohy-      °dO°°  °  O  °  °   o°o 
drates.     The  products  coming        ^b°**9?   *°°0  °  °  °O 
from  the  oxidation  of  fats  are        °0  °  °0  0o°o°Oo?}0 
water  and  carbon  dioxide.  o°°  oQ>°   •  °<.°°» 

Fats    are    digested    in    the  ?  *  °°°  Q°o  o°° 

small  intestines  by  the  diges-  o  o 

tive    fluid,    which    makes    an         FAT  GLOBULES  IN  MILK 
emulsion  out  of  the  fat.    This 

emulsion  can  pass  through  the  walls  of  the  intestine  and 
get  into  the  blood  by  way  of  the  thoracic  duct.  (Ask 
the  teacher  to  tell  you  more  about  it.)  Soaps  are  also 
made  in  the  intestine  from  fat  for  cleansing  purposes. 
When  soaps  are  made  glycerine  is  also  formed.  The 
body  uses  the  fat  for  making  heat,  which  is  done  by 
oxidation.  Fat  is  also  stored  up  in  various  parts  of  the 
body  for  protection  against  cold  and  against  possible 
injuries.  The  stored  fat  is  also  used  at  times  when  not 
enough  food  can  be  procured,  or  during  sickness,  for 
keeping  the  body  temperature  normal. 


u8  GENERAL   SCIENCE 

Because  of  the  great  amount  of  heat  produced  by  fat 
when  it  is  oxidized,  the  people  living  in  cold  countries, 
as  the  Eskimos  in  the  North,  must  eat  large  quantities 
of  fat  in  order  to  keep  warm.  They  become  accustomed 
to  digesting  large  quantities  of  fat  because  their  bodies 
need  it.  People  living  in  a  temperate  climate  like  that 
of  the  northern  United  States  usually  consume  more 
fats  or  fatty  foods  during  the  winter  season  in  order  that 
they  may  not  suffer  so  much  from  the  cold  weather.  In 
summer  or  in  warm  climates  people  naturally  do  not 
eat  much  fatty  food.  They  do  not  have  an  appetite 
for  such  food,  since  the  great  amount  of  heat  produced 
by  the  oxidation  of  fats  is  not  needed  during  that  time 
of  the  year.  The  appetite,  if  not  perverted  or  spoiled 
by  improper  eating,  is  a  comparatively  sure  guide  in 
determining  how  much  fatty  food  to  eat. 

(c)  Proteins.  —  Proteins  are  foods  which  contain  nitro- 
gen and  are  sometimes  called  nitrogenous  foods.  The 
elements  composing  protein  are  hydrogen,  nitrogen,  car- 
bon, oxygen,  and  some  sulphur.  Proteins  are  the  building 
foods.  They  form  about  80  per  cent  of  the  weight  of 
the  muscles  of  the  body  and  are  present  in  all  the  other 
tissues.  When  not  enough  carbohydrates  and  fats  are 
eaten  to  produce  the  heat  necessary  to  keep  the  body 
warm,  the  proteins  are  oxidized  to  make  heat.  But 
when  proteins  are  oxidized,  not  only  carbon  dioxide  is 
produced,  but  nitrogenous  wastes  also.  The  nitrogenous 
wastes  are  very  poisonous  to  the  body.  They  are  taken 
from  the  body  by  the  kidneys  and  the  sweat  glands,  and 
these  organs  —  especially  the  kidneys  —  may  become 
diseased  in  throwing  off  the  waste  produced  by  the  oxida- 
tion of  proteins.  For  this  reason  it  is  best  to  eat  just 
enough  carbohydrates  and  fats  to  produce  the  heat 


FOOD  1 19 

necessary  and  just  enough  protein  for  the  building  ma- 
terial. If  such  a  balanced  diet  is  eaten,  the  excretory 
organs  of  the  body  will  not  have  so  much  work  to  do 
and  so  will  remain  healthy.  Such  a  diet  will  also  lead  to 
a  more  nearly  perfect  health  of  the  entire  body. 

The  white  of  a  hen's  egg  is  almost  pure  protein  and 
water.  When  the  white  of  an  egg  is  heated  it  becomes 
solid;  such  a  process  is  known  as  coagulation.  Coagula- 


BEEF  IN   COLD  STORAGE 

tion  is  the  process  of  changing  protein  from  a  semi-liquid 
form  to  a  solid.  Clotting  of  the  blood  is  a  form  of  coagula- 
tion. The  protein  in  the  blood  —  called  fibrin  —  forms 
a  solid  stringy  material  and  encloses  the  red  and  white 
corpuscles.  Casein  is  the  coagulated  protein  of  milk, 
out  of  which  cheese  is  made.  Gluten  is  the  protein  of 
wheat.  It  can  be  obtained  by  chewing  whole  wheat 
grains  for  several  minutes  and  making  no  effort  to  swal- 
low. The  gummy  substance  left  in  the  mouth  is  largely 
gluten.  Gluten  can  also  be  obtained  from  flour  by 
taking  a  tablespoonful  of  flour  and  wrapping  it  in  a 


120 


GENERAL  SCIENCE 


piece  of  cloth;  then  wet  it  thoroughly  with  water  and 
squeeze  or  work  it  between  the  fingers  for  several  minutes, 
dipping  it  often  in  water  to  keep  it  moist.  The  substance 
left  in  the  cloth  after  such  a  process  is  gluten.  'Gluten, 
being  a  tough,  gummy  substance,  and  somewhat  elastic, 


POTATO 


CHEESE  (FULL  CREAM) 


EGG 


WHITE  BREAD 


RELATIVE  PROPORTIONS  or  DIFFERENT  NUTRIENTS  IN 
WELL-KNOWN  FOODS 

prevents  the  escape  of  carbon  dioxide  from  the  dough 
when  bread  is  permitted  to  rise. 

Just  enough  protein  should  be  eaten  for  the  growth 
of  the  bodily  parts  and  to  rebuild  partially  worn  out 
cells.  The  amount  needed  will  depend  upon  the  age  of 
the  person  and  the  kind  of  work  that  he  is  doing.  A 
person  working  in  an  office  or  in  school  does  not  require 
as  much  protein  as  a  person  who  is  engaged  in  hard 
physical  labor  like  shoveling  coal  or  working  on  the  rail- 
road. Men  who  are  engaged  in  hard  physical  work  can 
live  well  on  such  foods  as  meat  and  beans,  because  lean 
meat  and  beans  have  a  large  quantity  of  protein.  Protein 


FOOD  121 

in  beans  is  more  economical  for  use.  Protein  in  meat 
costs  from  three  to  five  times  as  much  as  the  same 
amount  of  protein  in  beans. 

80.  Water  and  Mineral  Foods.  —  The  unorganized  or 
mineral  foods  include  water,  common  salt,  calcium,  and 
iron   compounds.     These   are  eaten  in   large  quantities 
with   the   nutrients.     Water   is   often   taken   separately, 
during    meal    time    and   between   meals.     The    body   is 
about  65  per  cent  water.     What  is  the  weight  of  the 
water  in  the  body  of  a  person  who  weighs  150  Ibs?     About 
75  per  cent  of  the  beef  on  the  market  is  water;    90  per 
cent  of  blood  is  water. 

Use  of  Water.  —  Water  is  used  in  the  body  to  carry 
food  to  all  parts  and  to  every  cell.  What  is  the  name  of 
the  liquid  in  the  body  that  carries  the  food?  Water  is 
used  to  liquefy  the  foods  for  digestion,  so  that  they  can 
pass  through  the  walls  of  the  digestive  organs  into  the 
blood.  Water  keeps  the  body  in  a  flexible  condition  so 
that  it  does  not  become  stiff  and  rigid  like  dried  beef. 
The  water  in  the  muscles  permits  them  to  contract  and 
change  their  shape,  and  thus  enables  the  whole  body  to 
move  about.  Unless  a  large  percentage  of  the  body 
were  water  we  could  not  move  about  and  be  active  in 
our  work.  About  three  quarts  of  water  should  be  taken 
daily  by  each  adult.  These  three  quarts  include  the 
water  which  is  taken  separately  and  that  which  is  in  the 
foods  when  eaten. 

The  minerals  in  foods  are  used  to  form  the  framework 
of  the  body,  such  as  bone  and  connective  tissue,  which 
give  shape  to  the  body  and  hold  the  cells  in  place.  Lime 
and  phosphorus  help  to  form  bone. 

81.  Tests  for    Nutrients.  —  Foods  can  be   tested   for 
carbohydrates  by  placing  on  them  a  few  drops  of  dilute 


122  GENERAL  SCIENCE 

iodine  solution.  For  example,  take  a  piece  of  bread  and 
put  on  it  some  weak  iodine  solution.  The  color  of  the 
bread  will  become  blue  or  bluish  purple.  Beans  and 
cereals  of  all  kinds  can  be  tested  in  this  way  for  carbo- 
hydrates. (To  learn  just  the  effect  of  iodine  solution 
on  starch  in  foods,  put  a  little  corn  starch  into  a  test 
tube  and  add  some  water,  then  put  into  the  test  tube  a 
few  drops  of  iodine  solution  and  observe  the  color. 
This  will  serve  as  a  sample  color  in  testing  foods  for 
starch.) 

To  test  foods  for  protein,  observe  the  following:  Take 
a  piece  of  bread,  put  on  it  some  strong  nitric  acid;  if 
protein  is  present  the  bread  will  turn  yellow.  Now  add 
some  ammonium  hydroxide  and  the  yellow  portion  will 
change  to  orange  if  it  is  protein.  Other  foods  can  be 
tested  for  protein  in  the  same  manner. 

Foods  can  be  tested  for  fats  thus :  Take  a  small  quantity 
of  corn  meal,  place  it  on  white  paper,  and  put  the  white 
paper  with  the  corn  meal  on  it  into  an  oven  which  is  not 
quite  hot  enough  to  scorch  the  paper.  The  oil  in  the 
meal  will  make  a  spot  on  the  paper.  Other  foods  can  be 
tested  for  fats  in  the  same  manner. 

To  test  foods  for  sugar,  place  a  small  quantity  of  the 
food  in  a  test  tube  with  some  water,  and  put  into  it 
a  few  drops  of  Fehling's  solution.  Heat  the  mixture 
slowly  over  a  Bunsen  burner  or  alcohol  lamp  and  watch 
the  color  of  the  contents  in  the  test  tube  as  the  tempera- 
ture rises.  If  sugar  is  present  the  color  will  first  be  a 
greenish  yellow,  changing  to  yellow,  and  finally  to  brick- 
red  when  the  substance  begins  to  boil.  (To  be  sure  of 
the  colors  in  the  test  for  sugar  with  Fehling's  solution, 
make  a.  weak  solution  of  sugar  and  test  it  with  Fehling's 
solution,  observing  the  colors.) 


FOOD 


123 


82.  Fuel  Value  of  Foods.  —  Since  two  of  the  nutrients 
are  used  entirely  for  the  production  of  heat  in  the  body, 
and  since  the  other  one  is  often  used  in  a  large  quantity 
for  the  same  purpose,  the  fuel  value  of  foods  is  determined 
by  finding  how  much  heat  they  will  produce  when  oxi- 
dized or  burned.  In  order  to  determine  the  fuel  value 
of  foods  it  is  necessary  to  burn  them  in  an  apparatus 
known  as  the  bomb  cal- 
orimeter. This  is  a  very 
simple  instrument  com- 
posed of  an  inner  and 
outer  chamber 
with  a  space  be- 
tween for  water. 
The  food  to  be 
burned  is  placed 
in  the  inner 
chamber  and  a 
thermometer  is 
placed  in  the 
water  between 
the  inner  and 
outer  chamber. 

The  temperature  of  the  water  is  taken.  After  the  food 
is  burned  the  temperature  of  the  water  is  again  taken. 
The  weight  of  the  water  and  of  the  food  in  the  calo- 
rimeter must  be  known.  The  increase  in  temperature 
multiplied  by  the  weight  of  the  water  in  grams  will  be 
the  amount  of  heat  produced  by  the  quantity  of  food 
burned. 

The  food  calorie  is  larger  than  the  ordinary  or  common 
calorie.  The  food  calorie  may  be  defined  as  the  quantity 
of  heat  necessary  to  raise  the  temperature  of  one  kilogram 


BOMB   CALORIMETER  FOR   DETERMINING   THE 
FUEL  VALUE   OF   FOOD 

F  is  the  food  chamber;  W  is  the  water  for  re- 
ceiving the  heat  from  the  burning  food;  P  is 
packing  to  prevent  the  loss  of  heat;  V  is  the 
entrance  valve;  T  is  a  thermometer;  O  is  the 
tank  for  supplying  oxygen. 


124  GENERAL   SCIENCE 

of  water  one  degree  Centigrade.  The  reason  for  using  a 
large  calorie  in  measuring  the  fuel  value  of  foods  is  to 
avoid  large  numbers  in  recording  the  fuel  value. 

The  carbohydrates  produce  the  least  amount  of  heat 
when  oxidized,  and  so  in  order  to  produce  the  same 
amount  of  heat  more  of  that  nutrient  should  be  eaten 
than  of  the  other  two.  Fats  when  oxidized  produce 
about  two  and  one-fourth  times  as  much  heat  as  carbo- 
hydrates. Proteins  produce  about  one  and  one-half 
times  as  much  heat  as  carbohydrates  when  oxidized.  But 
since  protein  is  a  building  nutrient,  an  amount  only 
sufficient  for  the  growth  and  repair  of  cells  should  be 
eaten,  while  the  other  two  nutrients  should  be  eaten  for 
the  production  of  heat.  The  relative  amounts  of  carbo- 
hydrates and  fats  that  any  one  person  should  eat  will  be 
determined  by  the  climate  in  which  he  lives,  by  the  work 
done,  and  by  the  physical  condition  of  the  organs  of  the 
body.  Carbohydrates  and  fats  taken  in  the  right  pro- 
portion should  be  eaten  in  an  amount  sufficient  for  the 
production  of  just  the  necessary  heat  that  the  body 
requires.  Eating  the  proper  amount  of  each  nutrient 
will  give  the  bodily  organs  the  least  amount  of  work  to 
do  in  throwing  off  poisonous  waste  products. 

83.  Daily  Fuel  Needs  of  the  Body.  —  It  has  been 
stated  that  the  amount  of  food  eaten  daily  should 
vary  according  to  climate,  the  time  of  the  year,  the 
occupation,  age,  etc.  The  following  table  gives  the  fuel 
needs  of  the  body  at  various  ages  and  occupations:  — 

DAILY  CALORIE  NEEDS  (APPROXIMATELY) 

1.  For  a  child  under  two  years      900    Calories. 

2.  For  a  child  from  two  to  five  years 1200 

3.  For  a  child  from  six  to  nine  years 1500 

4.  For  a  child  from  ten  to  twelve  years 1800       " 


FOOD  125 

5.  For  a  child  from  twelve  to  fourteen  years  (women,  light 

work  also)    ..................     2100   Calories. 

6.  For  a  boy  twelve  to  fourteen  years,  girl  fifteen  to  six- 

teen, and  man  of  sedentary  habits  ........     2400 

7.  For  a  boy  fifteen  to  sixteen,  man  light  muscular  work       2400 

8.  For  a  man  at  moderately  active  muscular  work    .    .    .     2700 

9.  For  a  farmer,  busy  season     .........  3200  to  4000 

10.  For  ditchers,  excavators,  etc  .........  4000  to  5000 

11.  For  lumbermen    .................     5000 

84.  Bodily  Heat  Output.  —  Some  experiments  have 
been  conducted  to  determine  the  amount  of  heat  which 
escapes  from  the  body  every  hour.  The  following  table 
will  give  some  idea  of  the  average  escape  of  heat  from 
the  normal  body  while  asleep,  awake,  at  work,  or  at 
rest:- 

AVERAGE  OUTPUT  OF  HEAT  FROM  THE  BODY 
Condition  of  Muscular  Activities 

Average  Calories 
per  hour 

Man  at  rest  sleeping    .................  65 

Man  at  rest  awake,  sitting  up    .............  100 

Man  at  light  muscular  exercise  .............  1  70 

Man  at  moderately  active  muscular  exercise  .......  290 

Man  at  severe  muscular  exercise   ............  450 

Man  at  very  severe  muscular  exercise      .........  600 

In  order  to  determine  how  much  heat  is  given  out  by 
a  man,  all  you  have  to  do  is  to  calculate  the  number  of 
calories  given  out  for  the  hours  spent  in  the  various 
kinds  of  activities  during  the  twenty-four  hours.  For 
example:  Suppose  we  take  a  man  working  at  moderate 
labor,  who 

Sleeps  for  nine  hours    .........  9  X  65  calories     585  calories. 

Works  for  eight  hours  .........  8x290     "         2320       " 

Reading  and  at  rest  at  home  seven  hours.  7  X  100     "  700       " 


The  following  table  will  give  some  idea  of  the  relative 
amounts  of  the  nutrients  in  the  various  kinds  of  bread 


126 


GENERAL  SCIENCE 


TABLE  I 

COMPOSITION  OF  VARIOUS  SORTS  OF  BREAD  AND  SOME  OTHER  FOOD 
MATERIALS 


Food  Materials 

Num- 
ber of 
analy- 
ses 

Ref- 
use 

Water 

Pro- 
tein 

Fat 

Car- 
bohy- 
drates 

Ash 

Wheat  bread: 
From  hard  Scotch  Fife  spring  wheat 
Minnesota 

7  76 

42  82 

Entire-wheat  flour  

49.16 

7-45 

1.14 

41.73 

.52 

Standard  patent  flour  

44.13 

7-75 

.90 

46.90 

•32 

Second  patent  flour  
First  patent  flour  
From  Oregon  soft  winter  wheat 
Graham  flour  
Entire-wheat  flour  
Straight  grade  flour 

42.10 
44.40 

38.55 
39-95 

7-75 
7-48, 

6.  ii 

5-70 
5  41 

.72 
•  7i 

1.  12 
1.09 
89 

49.16 

47.14 

52.68 
52-39 
57  85 

.27 
•  27 

1-54 
-87 

From  Oklahoma  hard  winter  wheat 
Graham  flour  
Entire-wheat  flour  
Straight  grade  flour  
Straight  grade  flour  with   14    per 
cent  bran 

42.20 
4I-3I 
37-05 

43.20 

10.65 
10.60 
10.13 

9-5° 

1.  12 

1.04 
.64 

.84 

44.58 
46.11 
5i-i4 

45-55 

1-45 
•94 

•44 

.91 

Straight  grade  flour  with  7  per  cent 
germ 

38  oo 

ii  07 

I   13 

49.12 

.68 

From  miscellaneous  flours 
High  grade  patent  
Standard  grade  patent  
Medium  grade  patent  
Low  grade  patent    . 

32.9 
34-1 
39-1 
40.7 

8.7 
9.0 
10.6 

12.6 

•4 
-3 

.2 
.1 

56.5 
54-9 
48.3 
44-3 

-5 
-7 
9 
.3 

White  bread,  average 

198 

35-3 

9.2 

.3 

53.1 

.1 

Rolls 

20 

35-7 

8.9 

.8 

52.1 

.5 

Crackers  

71 

6.8 

10.7 

8.8 

71.9 

.8 

Macaroni  

ii 

10.3 

13.4 

•9 

74.1 

.3 

38  9 

4  7 

46  3 

2 

Rye  bread  
Rye-and-wheat  bread  

21 

35-7 
35-3 

9.0 
11.9 

.6 
.3 

53-2 
51.5 

•5 
.0 

Beef,  ribs 
Edible  portion 

ig 

71.7 

20.7 

6.7 

i.i 

As  purchased 

18 

11.7 

63.4 

18.3 

5-8 

I.O 

Mutton,  leg 
Edible  portion 

15 

63  2 

18  7 

17.5 

I.O 

As  purchased  
Cod  steaks 
Edible  portion  .  . 

IS 

I 

17.7 

51-9 
79-7 

15-4 
18.7 

14-5 
.5 

.8 

1.2 

As  purchased 

I 

9.2 

72.4 

17.0 

.5 

I.O 

Hens'  eggs 
Edible  portion  

60 

73-7 

13.4 

10.5 

I.O 

As  purchased  

II.  2 

65.5 

11.9 

9-3 

•9 

Butter  

II.O 

I.O 

85.0 

3-0 

Milk   whole 

87  o 

3  3 

4  ° 

5-O 

.7 

Potatoes 
Edible  portion  
As  purchased 

136 

2O.  O 

78.3 

62.6 

2.2 

1.8 

.1 

.1 

18.4 
14.7 

I.O 

.8 

Apples 
Edible  portion 

29 

84.6 

•4 

.5 

14.2 

•3 

As  purchased  

25.0 

63.3 

.3 

•3 

10.8 

.3 

Chocolate 
As  purchased  

2 

5-9 

12.9 

48.7 

30.3 

2.2 

FOOD  127 

and  in  some  other  foods.  By  a  careful  study  of  the 
table  one  can  determine  the  relative  nutritive  values  of 
the  different  kinds  of  bread  and  also  the  relative  nutritive 
values  of  the  breads  made  from  wheat  grown  in  different 
parts  of  the  United  States.  Compare  the  food  value  of 
bread  with  that  of  other  foods  by  making  a  study  of 
Table  I,  on  page  126. 

85.  Nutritive  Ratio.  —  Experiments  in  feeding  live- 
stock have  been  conducted  for  many  years  in  various 
parts  of  the  United  States.  Many  of  these  experiments 
have  been  conducted  by  the  Agricultural  Experiment 
Stations.  The  results  of  these  experiments,  showing 
how  to  feed  live-stock,  have  been  sent  to  the  farmers. 
Farmers  now  know  just  how  much  of  each  nutrient  to 
feed  their  horses,  cattle,  hogs,  poultry,  etc.,  in  order  to 
grow  healthy  animals  and  not  waste  any  food.  Many 
farmers  are  now  more  careful  about  feeding  their  animals 
than  they  are  about  the  diet  on  their  own  tables.  But 
people  in  the  cities,  who  know  little  about  feeding  animals, 
are  more  apt  to  waste  food  than  are  the  farmers,  in  the 
selection  of  their  diet.  Some  experiments  in  human  feed- 
ing have  been  conducted  in  order  to  educate  the  inhab- 
itants of  both  the  rural  districts  and  the  cities  in  the 
subject  of  foods.  Professors  Atwater,  Chittenden,  and 
Voit  are  noted  authorities  on  human  dietetics.  The  aver- 
age of  the  nutritive  ratios  obtained  by  these  three  men,  is 
i  to  6  for  adults.  The  ratio  i  to  6  means  that  one  part 
protein  to  six  parts  of  fats  and  carbohydrates  should 
be  eaten,  or  every  time  one  ounce  of  building  material 
(protein)  is  eaten  one  should  eat  six  ounces  of  fuel  food 
(fats  and  carbohydrates).  The  relative  amounts  of 
fats  and  carbohydrates  that  a  person  should  eat  depend 
upon  the  climate  and  the  physical  condition  of  the  indi- 


128  GENERAL  SCIENCE 

vidual.  The  nutritive  ratio  for  children  is  about  i  to  4.2. 
The  relative  amount  of  protein  in  the  diet  should  be 
gradually  reduced  from  the  time  of  childhood  to  maturity, 
at  which  time  the  ratio  should  be  made  comparatively 
constant  at  about  i  to  6.  A  slight  variation  should  be 
made  according  to  the  occupation  of  the  individual. 

If  the  foods  that  are  eaten  have  the  proper  nutritive 
ratio,  there  will  be  less  waste,  less  poison  for  the  body 
to  dispose  of,  and  the  body  will  be  well  nourished  and 
good  health  will  result.  The  nutritive  ratio  of  milk 
varies  from  i  to  4.2  to  i  to  5.  Wheat  bread  varies  from 
i  to  4.5  to  i  to  ii.  Corn  bread  has  a  nutritive  ratio  of 
about  i  to  7.  To  find  the  nutritive  ratio  of  any  food  in 
Table  I  (page  126),  multiply  the  percentage  of  fat  by 
2.25  and  add  the  product  to  the  percentage  of  carbo- 
hydrates, and  then  divide  the  sum  by  the  percentage  of 
protein.  The  result  will  be  the  number  of  parts  of  fats 
and  carbohydrates  to  one  part  of  protein.  For  example, 
milk  taken  from  the  table  has  3.3  per  cent  protein,  4.0 
per  cent  fat,  and  5.0  per  cent  carbohydrates.  Then  the 
nutritive  ratio  of  milk  is  3 .3  to  (4  X  2 . 2 5)  +  5  or  i  to  4. 2 .  To 
find  the  nutritive  ratio  from  Table  II  (page  129),  add  the 
calories  produced  by  the  fats  and  carbohydrates  and 
divide  the  sum  by  the  calories  produced  by  the  protein. 
The  nutritive  ratio  of  milk  in  Table  II  is  19  to  (52  +  29), 
or  i  to  4.3. 

86.  Varied  Diet.  —  By  varied  diet  we  do  not  mean  that 
we  should  vary  the  proportionate  amounts  of  the  three 
nutrients  —  carbohydrates,  fats,  and  protein.  But  the 
articles  of  food  containing  the  proper  nutritive  ratio 
should  be  changed  from  time  to  time  for  several  reasons, 
some  of  which  follow.  A  limited  variety  of  food  should 
also  be  eaten  at  each  meal.  If  only  one  thing  is  eaten 


FOOD 


129 


TABLE  II 
FOOD  VALUES,  UNITES,  AND  PRICES 


Name  of  Food 

Portion  containing 
100  Food  Units. 

Weight 
for  100 
calories 

Calories  furnished  by 

Price 
per 
Pound 

Protein 

Fat 

Carbo- 
hydrates 

i.  Animal 
Beef  (sirloin)  
Brisket  
Chicken 

Small  steak  
Ordinary  serving  

Ounces 
1.4 
i.  80 
3-2 
4-9 

2.1 
I.I 

4.1 
1.2 

6.8 
•97 

2.4 

0.44 
9-7 
•77 
4-9 

7-3 
3-5 
9-4 
27.0 
.62 
.56 

2.66 
ii. 
.96 
•9 
18. 
5-6 
3-62 
3-1 
.86 

15-2 

1-3 

3i 
42 
79 
95 
32 
28 
78 
35 
49 
18 
73 

o.S 
34 
25 
19 

3 
5 
6 
6 

20 

8 

21 
20 
10 
10 

25 

18 
ii 

10 
21 

9 

69 

58 

21 

5 
68 

72 

20 
65 
22 
82 

27 
99-5 

12 

73 

52 

7 
5 
3 
6 
63 
72 

18 
8 
5 

20 

14 

7 

i 
i 

7 
7 

Cents 
30. 
8. 
30. 
IS- 
30. 
25- 
90. 
18. 
25- 
18. 
20. 

35- 
4- 
25- 
5- 

i-5 

7- 
7- 
3- 
5- 
40. 

6. 

2-S 

4- 

12. 
IO. 

7-5 
i-5 

10. 

6. 
6. 
5- 

Codfish 

Eggs  
Ham  
Lobster 

i  large  egg  
Ordinary  serving  

2 

Large  serving  
i  dozen  

Oysters  

29 

Pork  (loin)  
Veal  (leg) 

Large  serving  

2.  Dairy  Products 
Butter  
Buttermilk  
Cheese  (American)  .  .  . 
Whole  milk  

54 

2 
29 

QO 
90 
91 

88 
17 

20 

61 

72 

85 

70 
61 
75 
88 
89 

100 

72 
84 

1  5  cubic  inch  

Small  glass  
Two 

3.  Fruits,  Nuts,  etc. 
Apples  
Bananas 

One  large  
One  large  
One  whole  

Watermelon  

Chocolate 

5  square  
Side  dish 

4.   Vegetable 
Beans  (baked)  
Cabbage  
Corn  meal 

4  servings  
Cereal  dish  
2  crackers  
5  average  servings  

Crackers 

Lettuce  
Oatmeal  
Potatoes  (boiled)  
Rice  
Sugar 

Cereal  dish  
3  teaspoonfuls  
4  average  servings  
Thick  slice  

Tomatoes  

Wheat  bread........ 

for  a  meal,  the  appetite  usually  ceases  before  a  sufficient 
quantity  of  food  has  been  taken  to  satisfy  the  needs  of 
the  body.  Since  every  article  of  food  needs  its  own 
active  principle  for  digestion,  and  since  the  glands  which 
secrete  the  digestive  fluids  can  secrete  only  a  limited 
number  of  enzymes  at  one  time,  the  number  of  different 
articles  of  food  eaten  at  one  meal  should  not  be  great, 
but  just  sufficient  to  cause  the  appetite  to  remain  normal 


130  GENERAL  SCIENCE 

until  enough  food  is  taken  to  nourish  the  body.  If  too 
great  a  variety  of  food  substances  are  taken  during  one 
meal,  a  part  of  them  will  go  undigested.  The  meats 
and  vegetables  should  be  changed  from  meal  to  meal, 
or  at  least  several  times  a  week.  A  normal  appetite  is  a 
comparatively  sure  guide  in  determining  the  kind  and 
amount  of  food  that  a  person  should  eat. 

87.  When  and  How  to  Buy.  —  Many  families  in  the 
cities    are    suffering   because    of    carelessness   in    buying 
foods.     Many  complaints  about  the  "high  cost  of  living" 
would  be  needless  if  more  people  would  make  a  careful 
study  of  how,  when,  and  what  to  buy  and  how  to  use 
the  foods  after  they  are  bought.     Foods  should  be  bought 
when  they  are  in  season.     "In  season"  is  the  time  when 
the  greatest  amount  and  the  best  quality  of  a  particular 
food  are  on  the  market;   its  price  will  then  be  the  lowest. 
Foods  which  spoil  easily  should  be  bought  only  in  such 
quantities   as   can  be   used   without  waste,   while   foods 
that  can  be  stored  without   loss   should   be   bought   in 
larger  quantities  and  direct  from  the  producer  if  possible. 
For  example,  a  man  in  Pittsburgh  bought  eggs  from  a 
farmer  when   they  were  plentiful  and  preserved   them. 
This  man  was  eating  twenty- cent  eggs  when  other  people 
were  paying  35  to  40  cents  a  dozen  for  them.     Potatoes, 
dried  fruits,  canned  goods,  and  cereals  can  be  purchased 
in  quantity  while  they  are  on  the  market  in  abundance. 
It  must  not  be  forgotten  that  a  proper  place  to  store 
food  must  be  had  when  it  is  bought  in  large  amounts. 
Cash  payments  will  get  more  food  for  the  money  spent 
than  time  payments. 

88.  Waste  in  Buying  and  in  Use. --There  are  some 
people  who   think  that  unless  they  are  paying  a  high 
price   they  are   not  getting  nutritious  foods.     Often  the 


FOOD  131 

less  expensive  foods  are  more  nutritious  and  will  make 
a  healthier  diet  than  the  costly  foods.  "Recent  studies 
have  shown  that  if  the  proper  attention  were  given  to 
the  tissue  and  fuel  value  of  foods,  the  people  of  this 
country  could  purchase  the  same  amount  of  nourishment 
that  they  now  take  for  $500,000,000  less  annually  than 
the  present  cost."  In  colleges  where  some  students  pay 
from  four  to  ten  dollars  per  week,  the  boys  anxious  to 
economize  board  themselves  in  their  rooms  for  one 
dollar  and  fifty  cents  per  week  and  some  for  less.  As 
an  experiment,  a  student  changed  from  the  expensive 
board  to  boarding  himself.  He  purchased  bread,  butter, 
cereals,  eggs,  fruit,  and  only  a  little  meat.  He  walked 
about  five  miles  per  day  for  exercise.  At  the  end  of 
the  first  four  weeks  he  had  gained  four  pounds.  His 
board  cost  him  i6|  cents  per  day  or  $1.17  per  week.  He 
also  took  the  highest  scholarship  rank  in  the  college. 

The  nutrients  in  such  foods  as  beef  sirloin,  fish,  and 
oysters  cost  more  than  in  any  other  form.  Twenty-five 
cents  worth  of  peanuts  have  fifty-three  times  as  much 
fuel  value  as  twenty-five  cents  worth  of  oysters.  By  a 
careful  study  of  the  figures  in  Table  II,  the  relative  cost 
of  the  nutrients  in  different  articles  of  food  can  be  learned. 
Figure  out  the  amount  of  food  that  can  be  purchased  for 
ten  cents  in  the  form  of  cereals  or  vegetables,  and  in  the 
form  of  meats,  and  compare  the  results.  Care  in  the 
selection  of  proper  foods  that  are  nutritious  will  save  many 
a  dollar. 

There  is  also  much  waste  in  the  care  and  preparation 
of  foods  in  the  home.  Much  loss  occurs  in  improper 
cooking.  Meats  especially,  when  overdone,  lose  much 
of  their  flavor  and  are  far  less  easily  digested  than  when 
they  are  cooked  rare.  The  reasons  for  cooking  meats 


132  GENERAL  SCIENCE 

are  that  the  muscle  fibers  may  be  loosened  and  softened, 
and  that  the  bacteria  and  other  parasites  in  the  meat 
may  be  killed  by  the  heat.  The  common  method  of 
frying  makes  foods  less  digestible.  Stewing  is  an  eco- 
nomical as  well  as  a  healthful  method.  Slow  boiling  and 
roasting  are  excellent  methods  of  cooking  meat.  The 
oven  should  be  heated  to  a  high  temperature  before  the 
roast  is  put  into  it.  The  heat  will  cause  a  crust  to  form 
on  the  outer  surface.  This  crust  prevents  the  escape  of 
the  juices  from  the  inside. 

Vegetables  are  cooked  so  that  the  walls  of  the  cells 
containing  starch  grains  may  burst  and  permit  the 
starch  to  be  easily  acted  upon  by  the  digestive  fluids  of 
the  body.  Boiling  water  will  dissolve  out  the  nutrients 
from  vegetables,  so  it  is  best  to  boil  them  rapidly  or  boil 
them  in  just  enough  water  to  prevent  burning.  Potatoes 
boiled  in  just  enough  water  to  prevent  burning  will  be 
dry  and  mealy.  They  will  have  a  good  taste  and  will  be 
easily  digested.  Vegetables  should  be  cooked  with  the 
outer  skin  left  on  when  this  is  possible. 

QUESTIONS    AND    EXERCISES 

1.  Point  out  the  ways  in  which  your  body  can  be  compared 
to  an  engine. 

2.  Name  the  activities  of  a  living  body  which  are  necessary 
for  life. 

3.  Compare    the   meanings  of    "nutrient"   and    "nutriment." 
(See  glossary.) 

4.  Name    some    pure    carbohydrates.     Do    you    get    carbohy- 
drates from  plants  or  from  animals? 

5.  Is  fat  used  for  the  same  purpose  in  our  bodies  as  carbohy- 
drates ? 

6.  Compare  the  uses  which  the  body  makes  of  proteins  with 
the  uses  made  of  fats  and  carbohydrates. 


FOOD  133 

7.  What  substances  are  foods  besides  the  nutrients  ? 

8.  From  Table  II  select  a  sufficient  amount  of  food  for  one 
meal  that  will  have  a  nutritive  ratio  of  i  to  5. 

9.  Select  enough  food  for  three  meals  for  five  people  that  will 
have  a  nutritive  ratio  of  i  to  6. 

10.  Determine  approximately  the  nutritive  ratio   of  the  last 
meal  you  ate. 

11.  From  Table  II  determine  whether  you  could  decrease  your 
cost  of  living  without  any  injury  to  your  body. 

12.  Keep  an  itemized  account  of  all  food  purchased  at  home 
and  see  if  any  improvement  could  be  made  in  quality  and  at  the 
same  time  make  a  reduction  in  the  cost. 


CHAPTER  XVI 
WATER 

89.   The  composition  of  water  can  be  determined  by 
decomposing  it  with  an  electric  current  after  a  few  drops 

of  acid  have  been  added  so  that 
it  will  conduct  electricity.  Two 
tubes  filled  with  water,  each 
one  containing  a  platinum  elec- 
trode, are  connected  with  an 
electric  battery  or  other  cur- 
rent-producing apparatus  with 
an  electro-motive  force  of  two 
or  more  volts.  As  the  water  is 
decomposed,  one  gas  will  col- 
lect in  one  of  the  tubes  and  .the 
other  gas  in  the  other  tube. 
When  these  gases  are  tested  it 
will  be  found  that  one  is  hydro- 
gen and  the  other  oxygen.  The 
tube  containing  hydrogen  will 
have  twice  as  much  gas  by  vol- 
ume as  the  one  containing  oxy- 
gen. This  shows  that  water  is 
composed  of  two  parts  hydrogen 
and  one  part  oxygen,  by  volume. 


gases  is  as  follows:    The   tube 
which  has  the  greater  amount  of  gas  is  supposed  to  con- 


WATER 


135 


tain  hydrogen.  If  it  is  hydrogen,  it  will  burn  with  a 
blue  flame  that  is  almost  invisible  in  daylight,  and  will 
produce  great  heat.  If  the  gas  escaping  from  the  tube 
containing  the  most  gas  is  lighted  and  a  larger  long  glass 
tube  lowered  so  as  to  surround  the  flame,  drops  of  water 
will  be  seen  to  collect  on  the  inside  of  the  larger  tube. 
This  water  is  a  result  of  the  union  of  the  hydrogen  with 
the  oxygen  of  the  air. 

The  gas  in  the  tube  containing  the  smaller  amount 
will  support  combustion,  if  it  is  oxygen.  If  a  glowing 
splinter  of  wood  is  held  at  the  end  of  the  tube  where  the 
gas  escapes,  it  will  burst  into  flame. 

Pure  hydrogen  can  also  be  obtained  by  placing  pieces  of 
zinc  in  a  bottle,  as  shown  in  the  illustration,  and  pouring 


PREPARING  HYDROGEN 

on  the  zinc  dilute  hydrochloric  acid.  Collect  the  gas  com- 
ing from  the  bottle  by  allowing  it  to  pass  through  a  tube 
into  another  bottle  containing  water  and  inverted  in 
the  pneumatic  trough.  Caution.  —  It  will  be  found  that 
if  this  hydrogen  gas  is  mixed  with  oxygen  and  a  lighted 
match  placed  at  the  mouth  of  the  bottle  an  explosion 
will  result,  so  the  gas  must  be  handled  with  some  degree 
of  care. 


136  GENERAL  SCIENCE 

90.  Sources  of  Water.  —  The  sun  is  the  great  natural 
energy  producer  for  the  earth.  The  heat  coming  directly 
from  the  sun  causes  great  quantities  of  water  to  evaporate 
from  the  land,  the  rivers,  the  lakes,  and  the  ocean.  Why 
does  more  water  evaporate  from  the  ocean  than  from 
elsewhere?  The  water  which  is  thus  evaporated  is 
carried  by  the  winds  to  various  parts  of  the  earth.  Warm 
air  can  carry  more  moisture  than  cool  air.  When  cool 
air  is  warmed  its  capacity  for  carrying  water  is  increased. 
When  warm  air  is  cooled  its  capacity  for  carrying  water 
is  decreased.  When  winds  from  the  ocean  pass  over  a 
high  mountain,  they  are  cooled  so  that  they  are  unable 
to  carry  the  heavy  load  of  moisture  which  they  brought 
from  the  ocean.  The  moisture  condenses,  forms  clouds, 
and  falls  as  rain. 

When  the  warm  winds  coming  from  the  south  are  grad- 
ually cooled,  their  capacity  for  carrying  moisture  is  de- 
creased, so  clouds  are  formed  and  rain  is  the  result. 
When  a  cold  wind  from  the  north  meets  a  warm  wind 
from  the  south,  clouds  are  formed  suddenly  and  heavy 
rain  falls.  Since  air  expands  when  it  is  heated,  it  is 
forced  upward  by  the  cooler  air  surrounding  the  heated 
area.  The  air  rising  rapidly  carries  a  large  amount  of 
moisture  with  it,  but  the  air  is  cooled  rapidly  in  the  high 
altitudes  and  clouds  are  formed.  Such  cloud  formations 
may  sometimes  produce  what  is  known  as  a  "cloud  burst," 
which  is  nothing  more  than  a  sudden  condensation  of  the 
moisture  in  the  air  and  the  descent  of  the  moisture  to 
the  earth  in  the  form  of  rain. 

The  continuous  evaporation  of  water,  the  distribution 
of  the  vapor  by  the  wind  from  place  to  place,  the  con- 
densation of  the  vapor,  the  formation  of  clouds,  and  the 
falling  of  rain  keep  the  water  moving  about  over  the 


WATER  137 

earth  from  place  to  place.  The  action  of  the  sun  on 
the  water  of  rivers,  lakes,  and  the  ocean  causes  the  land 
to  be  well  supplied  with  moisture,  which  makes  the  pro- 
duction of  both  plants  and  animals  possible. 

91.  Why  Water  should  be  Purified.  —  The  decaying 
matter  in  the  fields  and  woods  —  such  as  plants,  leaves  of 
trees,  and  animal  matter  on  the  surface  — permits  large 
quantities  of  poisonous  substances  and  bacteria  to  get 
into  the  water.  Many  of  these  bacteria  are  not  harmful, 
but  there  are  some  that  are  dangerous  to  health  and  are 
called  disease  germs.  Some  of  the  dangerous  substances 
which  get  into  the  water  from  the  surface  of  the  earth 
are  chlorine  compounds.  When  water  chemists  of  the 
cities  find  chlorine  compounds  in  the  water,  they  know  that 
more  or  less  decayed  animal  or  plant  matter  has  entered 
the  water.  There  are  various  disease  germs  which  can  get 
into  the  water  from  the  surface  of  the  land,  and  some- 
times these  germs  are  carried  beneath  the  surface  and 
may  flow  into  springs  and  wells.  One  of  those  that  can 
be  easily  carried  by  water  is  the  typhoid  germ,  or  the 
typhoid  bacillus. 

People  are  sometimes  careless  of  the  waste  matters  of 
a  patient  who  has  typhoid  fever.  This  waste  may  con- 
taminate the  water  of  their  wells.  These  germs  in  the 
well  water,  if  swallowed  by  a  person  in  drinking,  may 
produce  the  disease.  Sometimes  when  a  well  is  near  the 
house  and  the  waste  water  is  thrown  on  the  surface  of 
the  ground  or  poured  into  the  sink,  it  may  find  its  way 
into  the  well,  carrying  the  germs  with  it.  The  surface 
of  the  ground  or  the  soil  is  capable  of  oxidizing  or  destroy- 
ing millions  of  germs,  but  the  earth  beneath,  the  subsoil, 
will  not  destroy  disease  germs  readily,  and  so  they  may 
pass  through  the  soil  and  get  into  the  deeper  parts  of  the 


138  GENERAL  SCIENCE 

earth.    These  germs  will  flow  with  the  water  to  the  well, 
if  there  are  no  obstructing  niters. 


SOURCES  OF  CONTAMINATION  OF  CISTERN  AND  WELL  WATER 

The  illustration  shows  the  liability  of  contamination  from  surface 
drainage  and  from  entrance  of  filth  at  the  top. 

92.  Methods  of  Purification.  —  Boiling.  —  One  of  the 
simplest  methods  of  killing  disease  germs  in  water  is  by 
boiling  it.  Boiling,  however,  does  not  remove  the  disease 
germs,  but  simply  kills  them  and  leaves  them  in  the  water. 
Disease  germs  which  are  inclosed  in  an  extra  tough 
membrane  are  not  killed  unless  the  water  is  boiled  for 
15  minutes.  Boiling  does  not  always  remove  poisonous 
substances,  as  some  chlorine  compounds,  from  water. 

Distillation  is  a  process  of  purifying  water  by  changing 
it  into  steam  and  then  condensing  the  steam.  The 
condensed  steam  is  the  purified  water.  Distilled  water 
is  free  from  germs  and  various  other  compounds  which 
may  have  been  dissolved  in  it.  Distillation,  however, 
is  somewhat  expensive,  especially  for  private  use.  Most 


WATER 


139 


cities  require  the  manufacturers  of  artificial  ice  to  distill 
the  water  before  freezing  it,  in  order  that  it  may  be  free 
from  germs  and  other  impurities.  For  city  use,  distilla- 
tion of  water  is  impracticable  because  the  large  quantities 
of  water  used  would  make  it  too  expensive.  There  is 
another  method  which  is  almost  as  effective. 

Filtration  is  a  process  of  purifying  water  by  causing  it 
to  flow  through  sand  and  gravel.  A  great  number  of 
American  cities  are  using  the 
filtration  process  of  purification. 
It  prevents  a  great  number  of 
diseases,  and  especially  typhoid 
fever.  It  also  removes  some  of 
the  harmful  chemicals  which  are 
in  river  water.  There  are  small 
charcoal  and  stone  filters  which 


I 


SECTION  OF  A  SAND  FILTER 
Showing  impure  water  (top), 
sand,  gravel,  and  filtered  water. 


can  be  attached  to  the  water  pipes  in  the  private  home 
and  the  water  thus  purified  by  filtration.     These  filters 

must  be  cleaned  often 
or  they  will  become  a 
source  of  disease  in- 
stead of  preventing  it. 

93.  Use  of  Water 
While  Camping.  —  Since 
so  many  of  the  Ameri- 
can people  are  beginning 
to  spend  part  of  their 
vacation  in  the  open  air, 
along  some  lake  or 
stream,  it  is  very  im- 
portant that  they  should 
be  acquainted  with  some 
encounter  when  they  use 


A  DRIVEN  WELL  FOR  CAMPERS 


of   the   dangers   which    they 


140  GENERAL  SCIENCE 

water  in  such  localities.  Campers  often  contract  dis- 
eases from  the  use  of  surface  water,  river  water,  and 
sometimes  even  from  springs  or  from  a  near-by  well. 
There  are  several  ways  in  which  these  dangers  can  be 
avoided.  The  garbage  of  the  camp  should  either  be 
burned,  buried,  or  carried  quite  a  distance  from  the 
camp  to  prevent  flies  from  collecting  in  great  numbers. 
A  place  where  there  are  no  mosquitoes  should  also  be 
selected.  If  water  is  taken  from  a  running  stream,  it 


A  HILLSIDE  CUT  BY  THE  ACTION  OF  WATER 

should  be  boiled  before  using  it.  Water  taken  from  a 
well  or  spring  should  be  tested  before  using,  and  if  germs 
are  found  the  water  should  be  boiled.  If  there  is  no 
well  or  spring  near,  but  a  large  stream,  a  well  can  be 
driven  in  a  few  hours  near  this  stream  and  a  pump  put 
into  the  driven  well.  The  well,  of  course,  will  have  to  be 
driven  lower  than  the  water  in  the  stream.  The  water 
from  the  stream  will  filter  through  the  sand  and  gravel 
into  the  well,  which  will  usually  be  free  from  disease 
germs. 

94.   Water  a  Solvent.  —  Rain  water  is  slightly  acid, 
which  enables  it  to  dissolve  more  easily  the  rocks  and 


WATER  141 

mineral  salts  in  the  earth.  Water  has  aided  in  making 
the  deposits  of  mineral  salts  found  in  the  mountains  as 
well  as  in  lowlands.  Through  evaporation  and  through 
mixture  with  substances  that  will  not  remain  together 
in  solution,  the  salts  that  the  water  has  dissolved  have 


A  VALLEY  MADE  BY  EROSION 

been  deposited  in  the  bed  of  lakes  or  fissures  in  the  rocks 
which  the  water  once  covered.  If  the  larger  part  of  the 
mineral  in  solution  was  an  iron  oxide,  the  deposit  is  a  bed 
of  iron  ore.  Many  of  the  gold  and  silver  veins  in  the 
Rocky  Mountains  were  formed  by  the  action  of  water. 
Mineral  veins  are  also  sometimes  formed  by  precipita- 
tion. Ask  your  teacher  how  to  form  a  precipitate,  by 
pouring  two  solutions  together. 

If  the  surface  water  that  is  slightly  acid  flows  into  the 
ground  and  comes  in  contact  with  a  layer  of  limestone, 
the  acid  will  cause  the  limestone  to  be  decomposed  and 
gradually  carried  away  by  the  water.  After  this  action 


142  GENERAL  SCIENCE 

has  been  in  process  for  many  years,  an  opening,  called  a 
cave,  is  left.  There  is  in  Kentucky  a  large  limestone 
cave,  which  is  called  the  Mammoth  Cave.  Such  caves 
are  also  found  in  Virginia.  Sandstone  caves  also  are 
formed  in  the  same  manner  as  limestone  caves. 

Erosion  is  a  process  by  which  the  surface  of  the  earth 
is  worn  away  by  the  water;  the  rock  and  soil  are  dis- 
solved and  some  of  the  solid  material  also  is  carried  away 
by  the  physical  force  of  the  water.  The  Grand  Canyon, 
made  by  the  Colorado  River,  is  an  example  of  erosion. 
The  small  ravines  and  gullies  on  hillsides  where  the 
timber  has  been  removed  are  the  results  of  erosion. 
Farmers  need  to  guard  against  erosion  in  order  to  prevent 
the  soil  from  being  carried  away.  They  usually  protect 
the  soil  by  keeping  plants  or  grasses  growing  in  their  fields. 

95.  Physical  Properties  of  Water.  —  The  boiling  point 
of  water  at  sea  level  is  100°  C.  Since  the  boiling 
point  varies  with  the  pressure  of  the  air  or  other  gases 
on  the  water,  on  the  top  of  a  mountain  water  will  boil 
at  a  temperature  below  100°  C.  Water  freezes  at  o° 
C.  in  the  open  air.  Water  is  at  its  maximum  density 
at  4°  C.,  that  is,  a  cubic  centimeter  of  water  weighs 
more  at  4°  C.  than  at  any  other  temperature.  If  water 
at  a  temperature  of  4°  C.  is  heated,  it  will  expand.  If 
water  at  4°  C.  is  cooled,  it  will  expand  slowly  until  its 
temperature  is  o°  C.  At  o°  C.  water  freezes  and  increases 
in  volume  about  one-ninth.  Nine  cubic  feet  of  water, 
when  frozen,  will  become  10  cubic  feet  of  ice.  Which 
weighs  more,  a  cubic  foot  of  ice  at  o°  C.,  or  a  cubic  foot 
of  water  at  o°  C?  To  melt  one  gram  of  ice  80  calories 
of  heat  are  required.  How  much  heat  will  be  given  out 
when  one  gram  of  water  at,o°  C.  freezes?  To  change  one 
gram  of  water  at  boiling  point  into  steam  requires  536 


WATER  143 

calories  of  heat.     How  much  heat  will  be  given  out  when 
one  gram  of  steam  is  condensed? 

96.  Three  States  of  Water.  —  Water  at  ordinary  tem- 
peratures is  a  liquid.     The  liquid  can  be  changed  into  a 
solid  by  freezing.     While  water  is  freezing,  heat  is  being 
taken  from  it.     Heat  is  required  to  melt  ice,  hence  ice 
is  valuable  for  refrigeration.     Liquid  water  can  be  changed 
to  a  gas  by  the  addition  of  heat.     The  gas  is  called  steam. 

97.  Water    and    Climate.  —  Except    hydrogen,    water 
has  the  highest  specific  heat  of  any  substance  and  so  a 
large  quantity  of  heat  is  required  to  increase  the  tempera- 
ture of  inland  lakes  and  seas.     The  water  once  heated 
requires  a  long  time  for  the  heat  to  escape.     On  account 
of   this   property  of   water,   lakes    do   not   change    their 
temperature    suddenly    and    so    they    do    not    vary    in 
temperature    very    much    throughout    the    entire    year. 
For  this  reason  large  lakes  and  inland  seas  affect  the 
climate  of  the  country  .around   them:    the  summers  are 
not  so  hot;   the  spring  season  comes  rather  late;   and  the 
autumn  is  temperate.     On  account  of  the  constancy  of 
the  climate,  regions  around   large   bodies    of   water   are 
usually  healthy  places  in  which  to  live.     Blossoming  fruit 
trees  in  the  springtime  are  less  apt  to  be  frozen  if  they 
are  near  a  large  body  of  water. 

Ocean  currents  have  great  influence  upon  the  climate  of 
various  parts  of  the  earth.  The  Gulf  Stream,  flowing 
out  of  the  Gulf  of  Mexico  across  the  Atlantic  Ocean  to 
Europe,  makes  the  climate  of  Western  Europe  mild  and 
unchangeable.  The  Japan  current,  coming  across  the 
Pacific  Ocean,  touches  the  western  shores  of  North 
America  and  makes  a  tropical  climate  in  Southern  Cali- 
fornia and  a  very  mild  temperate  climate  in  Washington 
and  Oregon.  The  climate  along  some  coasts,  such  as 


144  GENERAL   SCIENCE 

the  New  England  States,  is  very  changeable.  The  wind 
coming  from  the  south  is  warm  in  winter,  while  the 
northwestern  winds  are  extremely  cold.  In  summer  a 
southern  wind  is  cool  and  a  northwestern  wind  is 
usually  warm.  Ask  your  teacher  to  explain  this.  The 
climate  of  islands  is  kept  nearly  constant  by  the  water 
around  them. 

QUESTIONS    AND    EXERCISES 

1.  Of  what  two  elements  is  water  composed  ? 

2.  Why  does  it  rain  more  on  the  western  slope  of  the  Rocky 
Mountains  than  on  the  eastern  slope  ? 

3.  Is  your  water  at  home  free  from  germs  and  harmful  com- 
pounds ? 

4.  What  are  the  ways  of  purifying  water  ?     Which  method  do 
you  use  at  home  ? 

5.  So  far  as  water  is  concerned,  what  are  the  dangers  while 
camping  ?     How  avoid  them  ? 

6.  Are  there  any  caves  and  valleys  where  you  live?     What 
made  them  ? 

7.  On  the  basis  of  your  own  experience,  is  a  cubic  foot  of  ice 
heavier  than  a  cubic  foot  of  water  ? 

8.  Where  does  the  water  of  the  Gulf  Stream  get  its  heat  to  warm 
Europe  ?     How  does  it  carry  this  heat  ? 

9.  Why  does  San  Francisco  have  a  warmer  climate  than  New 
York? 


CHAPTER   XVII 
THE   AIR 

98.  The  Air  a  Mixture  of  Gases.  —  The  air  is  com- 
posed of  79  per  cent  nitrogen,  20  per  cent  oxygen,  .03 
per  cent  carbon  dioxide,  some  water  vapor,  and  other 
gases.  These  gases  —  nitrogen,  oxygen,  and  carbon 
dioxide  —  are  mixed  together,  but  are  not  combined 
chemically.  When  we  breathe,  the  oxygen  is  separated 
from  the  nitrogen  in  our  lungs.  When  natural  gas  burns, 
oxygen  from  the  air  unites  with  the  carbon  that  is  in  the 
gas  to  form  carbon  dioxide.  To  prove  that  about  four- 
fifths  of  the  air  is  nitrogen,  try  the  following  simple 
experiment. 

Take  a  piece  of  yellow  phosphorus  about  the  size  of  a 
pea,  dry  it  with  filter  paper, 
and  place  it  on  a  prepared 
float  in  a  pneumatic  trough. 
Ignite  the  phosphorus  with 
a  match  and  invert  over  it  a 
cylindrical  glass  vessel.  The 
phosphorous  oxide  formed 
will  be  absorbed  by  the 
water.  The  water  will  slowly 

rise  in  the  vessel  as  the  oxy-     TAKING  OXYGEN  OUT  OF  THE  AIR 
gen  is  consumed.     The  gas 

remaining  in  the  glass  vessel  above  the  water  is  nearly 
pure  nitrogen.  Measure  the  gas  and  compare  its  volume 
with  that  of  the  entire  vessel.  This  experiment  gives 
evidence  of  what  per  cent  of  the  air  is  oxygen. 


146  GENERAL  SCIENCE 

99.  Movements  of  the  Air.  — Air,  like  the  flowing  brook 
and  the  waves  of  the  sea,  is  never  quiet  or  at  perfect  rest. 
If  it  moves  less  than  3  feet  per  second  its  movement  is 
not  perceptible  to  the  body.     Its  speed  varies  from  this 
unnoticeable  movement  to  that  of  the  raging  tornado. 
These    movements    are    caused   by   unequal   heating   in 
different  localities.     Air,  when  heated,  expands  and  be- 
comes less  dense  and  is  then  forced  away  by  the  cooler 
air.     The  air  at  high  altitudes  moves  more  freely  and 
faster  than  the  air  near  the  earth's  surface.     The  move- 
ments of  the  upper  air  can  be  detected  by  observing  the 
movements  of  clouds,  which  sometimes  travel  in  a  direction 
opposite  to  the  way  the  wind  is  blowing  near  the  ground. 

100.  Density  of  the  Air.  — The  air  surrounds  the  entire 
earth  and  when  it  is  spoken  of  as  a  whole  it  is  usually 
called  the  atmosphere.     It  extends  from  50  to  100  miles 
above  us.     It  is  most  dense  on  the  earth's  surface  at 
sea  level  and  rapidly  decreases  in  density  as  one  ascends. 
The  air   is  so  rare    on  the  tops   of  the   highest  moun- 
tains that  man  or  other  animals  cannot  go  there.     It 
is  even  difficult  for  some  people  to  stand  the  change  in 
the  density  of  the  air  while  crossing  the  Rocky  Moun- 
tains.    About    one-half    of    the    earth's   atmosphere    by 
weight    is    within    three    miles   of    the    earth's    surface. 
Some  air  is  in  water,  some  in  the  soil,  and  some  in  the 
deepest  openings  in  the  earth. 

101.  The  Weight  of  Air. --To  the  ordinary  observer 
air  does  not  seem  to  have  any  weight  or  to  offer  any 
resistance   to   objects  passing  through  it.     Recall  some 
experiences  that  you  have  had  and  some  unintentional 
observations  that  you  have  made  and  see  if  you  think 
that  air  has  no  weight.     A  person  running  or  riding  on 
a  bicycle  can  feel  the  air  pressing  against  him  with  con- 


THE  AIR 


147 


siderable  force,  especially  if  the  wind  is  blowing  toward 
him.  Everyone  has  experienced  the  force  of  the  wind 
when  he  was  passing  around  the  corner  of  a  building  on 
a  stormy  day.  You  have  seen  balloons  ascend  or  other 
objects  float  in  the  air.  The  balloon  ascends  because  it 

does  not  weigh  as  much  as 
the  air  which  it  displaces.  If 
a  pine  board  is  placed  at  the 
bottom  of  a  tank  of  water 
and  then  released,  it  will  soon 
rise  to  the  surface  of  the 


AIR  PUMP 

water.  Because  the  pine  board  is  not  so  heavy  as  the 
water  which  it  displaces,  the  water  forces  it  to  the  top. 
An  object  which  is  not  as  heavy  as  the  air  that  is  dis- 
placed by  it  will  ascend  for  the  same  reason  that  the 
board  does  in  the  water.  These  everyday  experiences 
give  some  evidence  that  the  air  is  composed  of  matter. 
Matter  is  anything  which  has  weight,  and  as  air  has 
weight  it  is  composed  of  matter. 

If  air  has  weight  then  it  should  be  possible  to  weigh 
it.  Let  us  see  if  we  can  weigh  air  on  scales.  Get  a 
rubber  bladder  from  a  football  or  basket-ball,  force  all 
the  air  out  of  it,  and  balance  it  on  delicate  scales  or  get 


148  GENERAL  SCIENCE 

its  weight  to  the  tenth  of  a  gram.  Now  pump  as  much 
air  into  the  bladder  as  it  will  hold  without  bursting  and 
weigh  it  again.  When  the  bladder  is  filled  almost  to 
bursting  capacity,  it  will  weigh  about  half  a  gram  more 
than  when  it  is  merely  full.  The  increase  in  weight  is 
due  to  the  weight  of  the  extra  air  forced  into  the  bladder. 
A  basket-ball  with  enough  air  in  it  to  be  used  in  a  game 
weighs  about  three  grams  more  than  it  does  when  it  is 
empty.  The  air  in  the  ball  is  more  dense  than  the  air 
outside.  The  air  that  is  forced  into  the  ball  to  make 
it  more  solid  adds  to  the  weight  of  the  ball. 

To  find  the  weight  of  a  given  volume  of  air,  try  the 
following  experiment.  Take  a  glass  bottle  or  other 
vessel  that  can  be  closed  air  tight,  determine  its  volume 
and  weigh  it  to  a  hundredth  of  a  gram.  Now  attach  it 
to  the  exhaust  air  pump  and  remove  as  much  air  as 
possible  and  then  weigh  it  again.  The  difference  in  the 
two  weights  is  the  weight  of  the  air  pumped  out.  Divide 
the  weight  by  the  number  of  liters  the  vessel  holds  and 
you  will  have  the  weight  of  the  air  per  liter.  A  liter  of 
air  at  standard  pressure  and  at  o°  C.  weighs  1.29  grams. 
Twelve  cubic  feet  of  air  weigh  a  pound.  Schoolrooms 
contain  from  600  to  1000  pounds  of  air.  Find  how 
much  your  schoolroom  holds. 

It  is  evident  from  these  experiments  that  air  can  be 
put  into  and  taken  out  of  a  vessel.  It  can  be  weighed 
and  handled  like  a  liquid  or  solid.  The  air  is  a  mixture 
of  gases,  it  is  matter,  it  has  weight,  and  it  is  held  on  the 
earth  like  any  other  substance.  It  is  drawn  toward  the 
center  of  the  earth  by  the  force  of  gravity. 

102.  Air  Pressure.  —  Pressure  is  force  per  unit  area. 
The  areas  most  commonly  used  are  the  square  inch  and 
the  square  centimeter. 


THE  AIR  149 

A  book  lying  on  the  desk  exerts  a  force  equivalent  to 
its  own  weight.  Water  in  a  vessel  exerts  a  force  against 
the  sides  and  bottom  of  the  ves- 
sel. Air  is  matter  and  so  it 
also  exerts  a  force  on  the  sides 
of  vessels  containing  it.  You 
have  experienced  this  with  bi- 
cycle tires  and  footballs.  Air  As  THE  AIR  is  EXHAUSTED  THE 
also  exerts  a  force  on  the  SHEET  RUBBER  is  FORCED  IN 

earth's  surface.     This  force  is  due  to  the  weight  of  the 
entire  atmosphere. 

If  a  rubber  membrane  is  stretched  across  a  large  opening 
in  a  glass  vessel  and  the  air  is  then  exhausted  from  it,  the 
membrane  will  be  forced  down  into  the  vessel  by  the  out- 
side air  pressure.  Again,  put  a  small  quantity  of  water  into 
a  tin  can  that  can  be  tightly  closed  by  a  cork,  and  heat 
it  to  boiling  point.  The  air  will  be  expelled  by  the  steam. 
While  the  water  is  still  boiling,  cork  the  can  tightly, 
remove  it  from  the  fire,  and  pour  cold  water  over  it. 
The  steam  inside  will  be  condensed  and  the  air  outside 
will  crush  the  can.  When  we  drink  lemonade  through 
a  straw,  we  exhaust  the  air  from  the  tube  and  the  pres- 
sure of  the  air  on  the  liquid  forces  it  up  through  the 
straw. 

The  height  to  which  air  will  force  water  in  a  tube  can 
be  determined  from  the  following  experiment.  Take  a 
glass  tube  34  inches  long  and  closed  at  one  end.  Fill 
the  tube  with  mercury,  close  the  end  with  your  finger, 
and  invert  it.  Now  place  the  bottom  into  a  dish  of 
mercury  and  remove  the  finger.  Notice  the  mercury 
in  the  tube;  it  will  fall  a  few  inches,  although  no  air 
can  get  in  at  the  top,  thus  making  a  perfect  vacuum  in 
the  top  of  the  tube,  The  weight  of  the  mercury  in  the 


GENERAL  SCIENCE 


tube  is  pressing  on  the  mercury  in  the  dish  and  the  weight 
of  the  air  is  also  pressing  on  the  mercury  in  the  dish. 
These  two  forces  per  unit  area  must  be  equal  as  the 

mercury  does  not  flow  into 
the  tube  or  out  of  it.  Hence 
the  air  pressure  on  the  mer- 
cury in  the  dish  is  equal  to 
the  pressure  of  the  mercury 
in  the  tube.  By  weighing 
the  mercury  in  the  tube,  it 
can  be  found  that  it  exerts  a 
pressure  of  about  15  pounds 
per  square  inch  when  it  stands 
at  a  height  of  30  inches. 
Then  the  air  must  also  have 
a  pressure  of  about  15  pounds 
per  square  inch  at  sea  level. 
That  is,  a  column  of  air  with 
a  cross-section  of  one  square 
inch,  extending  upward  as  far  as  there  is  air,  weighs  15 
pounds. 

If  you  have  any  doubt  as  to  whether  the  open  space 
above  the  mercury  is  a  perfect  vacuum,  just  incline  the 
tube  slowly  and  the  mercury  will  fill  the  open  space. 
If  there  were  any  air  or  other  substance  in  the  tube,  the 
mercury  could  not  go  to  the  top  of  it  when  the  tube  is 
inclined.  Now  hold  the  tube  erect  again,  and  the  mer- 
cury will  fall  to  its  former  position.  The  perpendicular 
height  of  the  mercury  is  what  determines  its  pressure  and 
not  the  length  of  the  column  when  the  tube  is  inclined. 
Since  mercury  is  13.6  times  as  heavy  as  water,  the  air 
will  hold  water  34  feet  high  in  a  tube  when  it  will  hold 
mercury  30  inches  high.  When  the  mercury  stands 


MEASURING  THE  AIR  PRESSURE 
WITH  MERCURY 


THE  AIR  151 

lower  than  30  inches  the  height  of  the  water  will  be  less 
than  34  feet.  In  the  year  1640  it  was  accidentally  learned 
that  air  would  not  lift  water  in  a  pump  more  than  32  feet 
above  the  surface  of  the  water  in  the  well.  But  at  that 
time  no  one  knew  why.  They  did  not  know  that  the 
downward  pressure  of  the  32  feet  of  water  was  equal  to 
the  pressure  of  the  air  at  that  particular  place.  Galileo, 
the  great  Italian  scientist,  was  living  at  that  time  and  he 
proceeded  to  investigate  this  strange  action  of  the  water. 
He  died  before  finishing  his  task,  and  so  it  was  left  to  his 
pupil,  Torricelli,  to  continue  the  investigation  and  learn 
the  truth  in  the  matter.  This  he  did  in  1643. 

Air  is  an  elastic  substance  and  so  it  can  be  compressed. 
The  air  at  sea  level  bears  the  weight  of  all  the  air  above 
it,  and  therefore  it  is  very  much  compressed,  and  the 
molecules  are  much  closer  together  than  they  are  in  the 
upper  regions  of  the  atmosphere.  Twelve  cubic  feet  of 
air  at  sea  level  weigh  a  pound,  but  twelve  cubic  feet  of 
air  at  an  altitude  of  16,000  feet  weigh  only  half  a  pound, 
and  at  an  altitude  of  15  miles  the  same  volume  weighs 
only  about  half  an  ounce.  This  shows  that  air  decreases 
rapidly  in  density  as  one  goes  to  higher  altitudes. 

This  rapid  decrease  in  the  density  and  pressure  of  the 
air  as  we  go  upward  explains  why  man  and  other  animals 
cannot  ascend  to  the  tops  of  the  highest  mountains; 
also  why  balloons  and  flying  machines  cannot  go  many 
miles  above  the  earth's  surface.  All  birds  and  flying 
devices  made  by  man  depend  upon  the  pressure  of  the 
air  to  sustain  them  and  keep  them  from  falling  to  the 
earth.  The  monoplanes  and  biplanes-are,  of  course,  heavier 
than  the  air  which  they  displace,  but  they  are  kept  from 
falling  by  being  moved  forward  at  a  great  speed  with 
the  planes  set  at  such  an  angle  that  the  air,  which  is  being 


152 


GENERAL   SCIENCE 


continuously  caught  under  the  planes,  causes  the  whole 
machine  to  be  lifted  before  the  air  has  time  to  move  from 
under  it. 

103.    Barometers  —  Kinds  and  Their  Uses.  —  There  are 
two  kinds  of  barometers,  the  mercurial  and  the  aneroid. 


U.  S.  GOVERNMENT  EXPERTS  TESTING  A  BALDWIN  DIRIGIBLE  AIRSHIP 

There  are  several  types  and  modifications  of  each  kind. 
Barometers  do  not,  as  some  think,  foretell  the  weather 
or  measure  the  height  of  mountains.  Barometers  measure 
only  one  thing,  and  that  is  the  air  pressure.  But  air  pres- 
sure and  weather  conditions  have  a  very  close  relation. 
By  hourly  readings  of  the  barometer  one  can  tell  whether 
the  mercury  is  falling  or  rising  and  how  fast.  A  falling 
barometer  indicates  foul  weather  and  a  rising  barometer 
indicates  the  approach  of  fair  weather.  A  comparatively 
sudden  drop  of  the  mercury  means  that  a  storm  is  ap- 
proaching. After  the  storm  is  past  the  mercury  will 


THE  AIR 


153 


rapidly  rise  again.  By  keeping  a  record  of  your  readings 
of  the  barometer  and  your  observations  of  the  weather, 
you  can  learn  to  foretell  the  weather  several  hours  or 
even  a  day  or  two  in  advance. 

Since  the  density  of  the  air  decreases  as  one  ascends  a 
mountain,  the  height  of  the  mountain  can  be  determined 
by  measuring,  with  a  barometer,  the  air  pressure  at  its 
base  and  on  its  summit.  The  mercury  falls 
about  one  inch  for  every  900  feet  of  vertical 
ascent.  If  the  mercury  reading  is  five  inches 
less  at  the  top  of  a  mountain  than  the  reading 
at  its  base,  how  high  is  the  mountain?  The 
height  of  buildings  and  hills  can  also  be  de- 
termined by  taking  the  readings  of  the  ba- 
rometer at  the  bottom  and  at  the  top.  The 
height  of  mountains  as  generally  given  indi- 
cates the  height  of  the  summit  above  sea 
level.  How  is  this  found? 

(a)  The  Mercurial  Barometer  is  essentially  the 
same  as  the  simple  barometer  tube  described 
in  §  102.  It  was  first  used  by  Torricelli  in 
1643.  The  modern  barometer  has  additional 
fixtures  to  prevent  the  mercury  from  spilling 
out  of  the  cup  or  cistern  and  for  accuracy  in 
reading  the  height  of  the  mercury  column.  This 
height  varies  from  29.2  to  30.5  inches,  or  from 
73  to  76.5  cm.,  in  localities  which  are  not  far 
above  sea  level.  The  reason  for  these  changes  A  MERCU. 
in  height  is  that  disturbances  of  the  atmos- 
phere affect  the  air  pressure  at  the  earth's  sur- 
face. Mercurial  barometers  can  be  made  the  most  accu- 
rately, and  are  used  in  the  United  States  Weather  Bureau 
offices  when  careful  observations  are  made. 


RIAL  BA- 
ROMETER 


154 


GENERAL  SCIENCE 


(b)  The  Aneroid  Barometer.  —  Since  the  mercurial 
barometer  is  long  and  inconvenient  to  carry,  geologists, 
surveyors,  and  mountain  climbers  commonly  use  the 
instrument  called  the  aneroid  barometer.  It  consists 
essentially  of  an  air-tight  cylindrical  box,  the  top  of 
which  is  a  metallic  diaphragm  which  bends  slightly  under 

the  influence  of  a  change 
in  the  atmospheric  pres- 
sure. If  the  air  pressure 
increases,  the  diaphragm  is 
pushed  slightly  inward;  if 
the  air  pressure  decreases, 
the  diaphragm  springs  out- 
ward. This  motion  of  the 
diaphragm  is  multiplied 
by  a  delicate  system  of 
levers,  and  is  communi- 
cated to  a  hand  which 


AN  ANEROID  BAROMETER 


Qver 


readings  are  made  to  correspond  to  the  readings  of  a 
mercury  barometer.  There  are  aneroid  barometers  made 
so  sensitive  that  they  will  indicate  a  change  in  pressure 
when  they  are  moved  from  a  table  to  the  floor.  The 
weather  conditions  are  printed  on  the  face  of  these  ba- 
rometers because  the  barometric  readings  and  weather 
conditions  usually  agree. 

Some  aneroid  barometers  have  two  hands,  one  fixed 
and  the  other  movable.  The  fixed  hand  is  set  over  the 
movable  one  at  a  certain  hour  and  in  reading  the  instru- 
ment one  can  tell  whether  the  air  pressure  has  increased 
or  decreased  since  that  hour,  for  the  movable  hand  will 
change  its  position  as  the  atmospheric  pressure  changes. 

Some  aneroid  barometers  are  made  in  the  shape  of  a 


THE  AIR  155 

watch  and  are  convenient  to  carry.  The  number  of  feet 
above  sea  level  is  marked  on  the  dial,  so  that  one  can 
determine  the  elevation  simply  by  looking  for  the  num- 
ber to  which  the  hand  points.  These,  however,  must 
be  set  with  the  mercury  barometer  before  starting  on  a 
trip  to  measure  elevation;  or  if  the  reading  is  taken  at 
the  base  of  a  hill  and  then  at  its  top,  the  height  of  the 
hill  above  the  plain  can  be  determined,  but  not  its  height 
above  sea  level. 

The  barograph  is  a  form  of  the  aneroid  barometer. 
Instead  of  having  a  hand  moving  around  a  dial  to  indi- 
cate the  pressure,  the  barograph 
has  an  arm  with  a  pen  at  the 
end,  which  writes  the  air  pres- 
sure on  a  sheet  of  paper  pre- 
pared for  it.  This  sheet  of  paper 
has  the  hours  of  the  day  and  the 
inches  printed  on  it,  and  is  A  BAROGRAPH 

fastened  on  a  roller  which  is  turned  by  clockwork.  As 
the  hours  pass  the  roller  turns  and  an  ink  line  is  made  on 
the  paper,  indicating  the  air  pressure. 

104.  Air  Currents.  —  The  atmosphere  is  constantly 
in  motion,  moving  in  various  directions.  When  the  air 
is  rising  in  one  locality,  it  is  descending  in  another. 
When  the  air  near  the  surface  is  moving  north,  a  current 
above  it  is  moving  south.  Currents  above  each  other 
are  usually  moving  in  opposite  directions.  The  two 
principal  causes  of  the  air  movements  are:  (i)  The 
unequal  heating  of  the  air  by  the  earth's  surface  and  (2) 
the  varying  amount  of  moisture  or  water  vapor  in  the  air. 
Either  one  of  these  causes  affects  the  air  pressure  and 
hence  affects  the  barometric  reading.  The  wind  blows 
toward  the  place  where  the  barometer  reads  low  and 


156  GENERAL  SCIENCE 

from  the  place  where  the  barometer  reads  high.  These 
places  in  the  air  which  cause  a  high  and  low  reading  of 
the  barometer  move  across  the  United  States  from  west 
to  east.  Rain  or  cloudy  weather  usually  follows  a  low 
pressure  and  clear  weather  follows  a  high  pressure.  The 
air  in  a  low  pressure  center  is  usually  rising  and  cooling, 
and  so  clouds  are  formed,  while  in  a  high  pressure  center 
the  air  is  falling  and  getting  warmer,  so  instead  of  forming 
clouds  it  takes  up  moisture  and  is  a  drying  wind. 


A  BIPLANE  JUST  LEAVING  THE  GROUND 

Aeronauts  who  travel  in  balloons,  airships,  or  aero- 
planes have  to  study  air  currents.  The  lack  of  a  knowl- 
edge of  air  currents  has  caused  the  death  of  many  airmen. 
The  aeroplane  passing  from  one  current  into  another 
may  plunge  to  the  ground,  if  the  current  just  entered  is 
moving  in  the  same  direction  as  the  machine.  Balloon- 
ists  control  their  direction  by  ascending  or  descending 
until  they  get  into  a  current  going  in  the  direction 
that  they  wish.  The  operators  of  airships  have  to  be 
careful  about  passing  from  one  current  into  another  or 
their  machine  may  take  a  sudden  plunge  to  the  earth. 


THE  AIR  157 

105.  Rain,  Snow,  Dew,  and  Frost.  —  The  heat  of  the 
sun  causes  continuous  evaporation  of  the  water  of  the 
oceans,  lakes,  and  rivers,  and  some  moisture  evaporates 
from  the  land  and  from  plants.  This  water  vapor  is 
carried  by  the  air  to  various  parts  of  the  earth.  Warm  or 
hot  air  can  carry  more  water  vapor  than  cool  or  cold  air 
can.  The  amount  of  water  vapor  in  the  air  varies  from 
day  to  day.  Sometimes  the  air  is  very  dry  and  at  other 
times  it  has  more  moisture  than  it  can  carry. 

To  prove  that  there  is  moisture  in  the  air  when  there 
seems  to  be  none,  let  us  recall  some  of  our  experiences. 
In  summer  the  air  is  warm  and  usually  has  a  great  amount 
of  moisture  in  vapor  form  which  is  invisible.  If  this  air 
is  cooled,  it  cannot  hold  its  moisture  in  the  invisible  form. 
The  vapor  will  collect  in  drops  on  cool  objects  like  the 
outside  of  a  vessel  containing  ice  water.  Cool  water 
just  taken  from  a  well  in  summer  and  poured  into  a  metal 
bucket  will  cause  drops  of  water  to  collect  on  the  outside 
of  the  bucket.  These  drops  are  formed  from  the  con- 
densed vapor  of  the  air.  If  you  want  to  see  these  drops 
of  water  form,  pour  a  quantity  of  ice  water  into  a  metal 
vessel.  When  the  water  vapor  of  the  air  condenses  on 
the  cool  grass  or  other  objects  at  night,  we  call  it  dew. 
If  it  is  sufficiently  cold  to  freeze  the  dew,  we  have 
white  frost. 

When  air  has  all  the  water  vapor  that  it  can  hold 
without  condensing  it,  it  is  said  to  be  saturated.  If  warm 
air  is  cooled  enough,  the  saturation  point  will  be  reached, 
and  if  the  cooling  is  then  continued  the  vapor  will  collect 
in  small  drops.  If  these  drops  collect  on  objects  they 
form  dew,  but  if  they  continue  to  float  about  in  the  air 
they  form  mist,  fog,  or  clouds.  When  air  is  saturated, 
it  is  at  the  dew  point.  Dew  point  is  that  condition  of 


158 


GENERAL  SCIENCE 


the  atmosphere  at  which  the  water  vapor  begins  to  collect 
into  droplets  of  water,  becomes  visible,  and  forms  fog  or 
clouds.  If  cooling  is  continued  after  the  dew  point  is 
reached,  heavy  clouds  will  be  formed,  the  drops  will  be 
too  heavy  for  the  air  to  carry,  and  they  will  fall  as  rain. 
If  the  air  is  below  freezing  temperature,  the  condensed 
vapor  will  be  frozen  and  snow  or  hail  will  fall. 

The  hygrometer  is  an  instrument  used  to  determine  the 
per  cent  of  moisture  in  the  air,  that  is,  to  ascertain  how 
near  the  air  is  to  the  dew  point.  The  hy- 
grometer determines  the  humidity  of  the 
air.  Humidity  is  indicated  on  the  instru- 
ment in  per  cent.  Humidity  is  the  per  cent 
of  water  vapor  in  the  air,  or  it  is  the  amount  of 
vapor  present  compared  to  the  amount  of  vapor 
that  the  air  can  hold  at  a  given  temperature. 
If  the  humidity  is  75  per  cent  at  a  tem- 
perature of  85°  F.,  that  means  that  the  air 
has  three-fourths  as  much  water  vapor  as  it 
can  hold  at  that  temperature.  If  the  tem- 
perature rises,  the  humidity  will  decrease  unless  more 
water  vapor  is  added  by  evaporation.  If  the  temperature 
falls,  the  humidity  may  increase  until  it  reaches  100  per 
cent,  when  condensation  will  occur;  100  per  cent  humidity 
is  dew  point. 

106.  Isobars  and  Isotherms.  —  Isobars  are  the  lines 
drawn  on  weather  maps  to  connect  places  having  the 
same  barometric  reading  at  a  given  time.  Since  the  128 
Weather  Bureau  stations  are  at  various  altitudes,  the 
barometers  in  the  different  offices  have  varied  readings 
and  would  not  mean  anything  if  they  were  put  on  the 
maps  as  they  are  read;  so  the  readings  are  reduced  to 
what  they  would  be  if  the  stations  were  at  sea,  level.  ISO- 


HYGROMETER 


THE   AIR 


159 


bars  have  no  definite  direction,  but  they  run  north  and 
south  more  often  than  any  other  way.  Sometimes  they 
form  circles.  They  are  indicated  on  the  weather  maps 
by  solid  black  lines. 

Isotherms    are    lines    connecting    places    having    equal 
temperatures  at  the  same  time.     Their  general  direction 


WEATHER  BUREAU  INSTRUMENTS  AT  THE  ANNUAL  EXPOSITION, 
PITTSBURGH,  PA. 

is  east  and  west,  but  they  shift  to  the  north  or  south 
according  to  the  elevation  of  the  country  and  the  direc- 
tion of  the  winds.  The  isotherms  now  put  on  the  weather 
maps  indicate  the  temperatures  which  are  multiples  of 
ten.  They  are  indicated  on  the  weather  maps  by  dotted 
lines. 

107.  Weather  Maps.  —  In  128  different  places  in  the 
United  States  are  Government  Weather  Bureau  Stations, 
at  each  of  which  accurate  observations  of  the  weather 
are  made.  These  observations  consist  of  reading  the 
barometer  and  thermometer,  ascertaining  the  humidity 
of  the  air  and  the  amount  of  rainfall  or  precipitation 


i6o 


GENERAL   SCIENCE 


since  the  last  observation,  and  determining  the  direction 
and  velocity  of  the  wind.  These  results  are  then  tele- 
graphed twice  each  day  to  the  chief  official  in  the  Weather 
Bureau  office  at  Washington.  From  these  reports  the 


;  dotted  black  licet  connect  places  haying 
temperature;  arrows  point  in  direction  wind  in  bio  win 
O  dear;  ©  partly  cloudy;  •  cloudy;   R  rain;  S 
HIGH  indicates  center  of  anticyclone,  or  high-pr 


WEATHER  MAP 

Isotherms,  dotted  lines,  drawn  for  every  10  degrees;  and  isobars,  unbroken 
lines,  drawn  for  every  tenth  of  an  inch.  Line  of  arrows  indicates  the 
ordinary  path  across  the  U.  S.  of  this  type  of  low.  Such  lows  usually 
advance  at  the  -rate  of  about  30  miles  an  hour. 

chief  officials  predict  what  the  weather  is  going  to  be  in 
the  near  future.  In  the  United  States  the  general  move- 
ment of  the  winds  is  from  west  to  east,  and  if  a  certain 
kind  of  weather  prevails  anywhere  in  the  west,  it  is  possi- 
ble that  it  will  advance  eastward,  but  many  modifications 
may  occur.  So  many  influences  change  atmospheric 
conditions  that  infallible  predictions  cannot  be  made. 
But  the  Weather  Bureau  predictions  do  prove  true  often 


THE  AIR 


161 


enough  to  save  many  lives  and  prevent  the  destruction 
of  much  property. 

Each  local  Weather  Bureau  office  receives  from  the 
other  offices  the  same  reports  that  are  sent  to  Washington. 
From  these  reports  the 
local  official  predicts  the 
weather  for  his  locality 
and  prints  a  daily 
weather  map.  The  pre- 
dictions are  printed  in 
the  daily  newspapers 
and  on  cards  and  on  the 
maps  sent  out  from  the 
Weather  Bureau  office. 
By  a  careful  study  of 
these  reports  and  the 
daily  maps  one  can  soon 
learn  to  foretell  the  prob- 
able weather  conditions 
of  the  folio  wing  day.  The 
many  signals  and  lines 
on  a  weather  map  are  all 
explained  at  the  bottom 
of  each  map.  To  under- 
stand the  map  it  is  necessary  to  become  familiar  with  the 
signals  and  the  meaning  of  the  numbers  and  lines  on  it. 
The  words  "low"  and  "high"  refer  to  the  reading  of  the 
barometer.  The  word  "low"  is  in  a  low  pressure  center 
and  the  word  "high"  in  a  high  pressure  center.  Cloudy 
and  unsettled  weather  follows  a  "low"  center  and  fair 
weather  follows  a  "  high  "  center.  The  winds  blow  toward 
a  "low"  center  and  then  rise,  and  they  descend  at  a 
"high"  center  and  blow  from  it  toward  the  "low"  centers. 


PUBLIC  WEATHER  "  CAB  " 
Showing  the  hygrometer,   barometer, 
rainfall  gauge,  thermograph,  and  maxi- 
mum and  minimum  thermometers. 


162 


GENERAL   SCIENCE 


QUESTIONS    AND    EXERCISES 

1.  What  is  the  difference  between  a  compound  and  a  mixture 
of  elements  ? 

2.  Is  the  air  a  mixture  of  gases  or  a  compound  ? 

3.  Give  the  approximate  composition  of  the  air. 

4.  Compare   the  vertical  extent   of   the  atmosphere  with   the 
height  of  the  highest  mountain. 

5.  Why  does  a  person's  nose  bleed  while  climbing  a  high  moun- 
tain? 

6.  What  causes  a  balloon  to  ascend  ? 

7.  Which  is  the  heavier,  a  balloon  ascending  or  an  equal  volume 
of  air  ? 

8.  Which  is  the  heavier,  a  bicycle  tire  pumped  full  of  air  or  an 
empty  one  ?     Swimming  wings  full  of  air  or  empty  ones  ? 

9.  What  is  the  approximate  air  pressure  in  your  schoolroom? 
Is  it  less  than  at  sea  level  ?     Why  ? 

10.  Which  is  the  greater,  the  downward  pressure  of  the  mercury 
in  a  barometer  or  the  pressure  of  the     ( 

air  around  the  barometer  ? 

11.  When     you     drink     a    liquid 
through    a    tube,    what    causes     the 
liquid   to   rise? 

12.  What  are  barometers  used  for  ? 

13.  What  causes   winds?     Which 

bring   rain?     Do   winds  carry  A 


winds 

heat? 

14. 


I 


B 


Explain  the  formation  of  dew. 
Make  some  dew  form  by  placing  very 
cold  water  or  ice  in  a  metal  vessel. 

15.  What  do  isobars  and  isotherms 
indicate  on  weather  maps? 

16.  Explain    the    meaning    of   the 
words,  "high"   and   "low"   on  weather  maps. 

17.  What  kind  of  weather  usually  accompanies  a  "high"  ?  "low"? 


CHALKED  PLATES  from  which 
the  cast  is  made  for  print- 
ing the  Weather  Maps. 
A,  is  the  blank  form;    B, 

after  the  map  characters  have 

been   cut    out  of  the    chalk 

down  to  the  steel. 


CHAPTER  XVIII 
SOME   PROPERTIES    OF   GASES 

108.  Gas  Pressure.  —  We  have  already  learned  that 
substances  are  composed  of  very  minute  particles  called 
molecules  and  that  these  molecules  are  in  motion.  The 
molecules  of  water  are  so  far  apart  that  molecules  of 
salt  or  sugar  can  occupy  the  spaces  between  them  when 
salt  and  sugar  are  dissolved  in  the  water.  The  mole- 
cules of  gases  are  farther  apart  than  those  of  water,  and 
they  move  about  faster  than  the  molecules  of  water. 
When  two  gases  are  mixed,  the  molecules  of  the  one 
occupy  the  spaces  between  the  molecules  of  the  other. 
Under  ordinary  conditions  the  two  gases  will  remain 
mixed.  Air  is  an  example  of  such  a  mixture  of  gases. 
Since  molecules  cannot  be  seen  with  the  best  microscopes, 
it  is  evident  that  they  must  be  very  minute,  and  the 
number  of  them  contained  in  a  cubic  centimeter  of  any 
substance  is  enormous.  It  may  be  that  a  thousand 
molecules  laid  side  by  side  would  not  make  a  speck  long 
enough  to  be  seen  with  a  good  microscope. 

That  molecules,  even  in  a  quiet  room,  are  in  contin- 
uous and  quite  rapid  motion  can  be  proved  by  recalling 
some  of  our  experiences.  If  an  ammonia  bottle  is  opened 
or  the  gas  turned  on  without  lighting  it,  the  odor  in  a 
very  short  time  will  have  become  perceptible  in  all  parts 
of 'the  room.  This  shows  that  enough  of  the  molecules  of 
the  gas  to  affect  the  nerves  of  smell  have  moved  across 
the  room.  These  molecules,  being  in  motion  and  travel- 
ing at  high  speed,  strike  against  one  another  and  against 


164 


GENERAL   SCIENCE 


STEAM  GAUGE 


other  objects.  Since  they  are  so  numerous  and  strike 
against  the  wall  of  the  vessel  containing  them,  they 
produce  what  is  called  pressure.  It  is  like  a  continuous 
pushing  against  a  wall.  If  a  stream  of  water  from  a 
hose  is  directed  against  a  wall,  it  exerts  a  continuous 
force  due  to  the  water  molecules 
striking  the  wall.  The  air  exerts  a 
pressure  of  15  pounds  per  square 
inch  against  the  walls  of  a  room  at 
sea  level.  Within  the  tube  of  an 
automobile  tire  the  molecules  of  air 
may  produce  a  pressure  of  100 
pounds  or  more  per  square  inch, 
and  in  a  steam  engine  the  pressure 
of  the  steam  may  be  200  pounds  per 
square  inch.  The  steam  made  from 
one  cubic  centimeter  of  water  will 
occupy  1600  cubic  centimeters  of 
space  when  under  about  15  pounds 
pressure.  So  in  steam  the  mole- 
cules are  1600  times  as  far  apart  as 
they  are  in  water  and  are  moving 
much  faster  than  they  do  in  water. 
Steam  engines  have  a  steam  gauge 
to  measure  the  molecular  pressure  of  the  steam.  There  is 
a  pressure  gauge  on  the  carbon  dioxide  tank  of  the  chemi- 
cal wagon  of  fire  companies.  These  gauges  in  principle 
are  very  much  like  an  aneroid  barometer.  Mercury 
gauges  are  also  sometimes  used;  in  these  the  gas  lifts  a 
column  of  mercury.  Every  two  inches  of  the  mercury 
column  is  approximately  equal  to  one  pound  of  pressure 
per  square  inch.  The  object  in  measuring  the  pressure 
of  gases  is  to  prevent  explosions. 


INTERIOR  OF  STEAM 
GAUGE 


SOME   PROPERTIES   OF   GASES  165 

109.  Boyle's   Law.  —  //  the  temperature  remains  con- 
stant, the  pressure  of  a  gas  varies  inversely  as  the  volume. 
If  a  cubic  foot  of  gas  is  forced  to  occupy  half  as  much 
space,  the  pressure  will  be  doubled.     If  the  pressure  is 
increased  from  10  pounds  to  30  pounds,  the  volume  of 
the  gas  will  be  one-third  of  what  it  was.     We  have  learned 
that  the  pressure  of  a  gas  is  due  to  the  blows  struck  by 
an  enormous  number  of  molecules  moving  at  high  speed. 
To  decrease  the  volume  one-half  is  to  double  the  density, 
and  when  double  the  number  of  molecules  strike  against 
the  same  area  of  the  surface  of  the  containing  vessel  the 
pressure  is  doubled.     By  calculation  it  has  been  found 
that  air  molecules  under  normal  conditions  move  at  the 
rate  of  about  445  meters  (1390  feet)  per  second,  while 
hydrogen  molecules  have   the  enormous  speed  of   1700 
meters  (5500  feet)  per  second.     The  speed  of  a  cannon- 
ball  is  seldom  greater  than  800  meters  per  second.     Since 
molecules  move  at  such  high  speed,  it  is  easy  to  under- 
stand   why   gases   produce   pressure    and    move    almost 
instantly   into    the   space   left   by   the   rising  piston  of 
an  air  pump,  and  why  any  gas  always  fills  completely 
the  vessel  containing  it. 

110.  Compressed  Gases.  •*-  Gases  are  perfectly  elastic 
and  can  be  compressed  or  made  more  dense;    that  is,  a 
given  weight  of  gas  can  be  made  to  occupy  less  space  if 
pressure  is  put  upon  it.     According  to  Boyle's  law,  if 
two  cubic  feet  of  gas  are  made  to  occupy  only  one  cubic 
foot  of  space,  the  pressure  of  the  gas  on  the  sides  of  the 
containing  vessel  will  be  doubled  if  the  temperature  is 
constant. 

The  discovery  of  this  property  of  gases  has  been  very 
useful.  Compressed  air  is  one  of  the  best  springs  that 
can  be  used.  It  would  not  be  very  comfortable  to  ride 


i6.6  GENERAL  SCIENCE 

on  bicycles  or  in  automobiles  if  it  were  not  for  the 
condensed  air  in  the  tires,  making  them  act  as  springs. 
The  Westinghouse  air-brake,  which  is  used  on  trains  and 
street  cars,  depends  upon  compressed  air  for  its  opera- 
tion. Compressed  air  is  also  used  in  drilling  and  riveting 
machines,  without  which  modern  skyscrapers  reinforced 
with  steel  could  not  be  built.  Many  kinds  of  hammering 
and  stone-cutting  machines  are  operated  by  compressed  air. 

The  gas  formed  by  the  explosion  of  gasoline  vapor  in 
a  gasoline  engine  requires  more  space  than  the  vapor, 
and  so  it  sets  the  piston  of  the  cylinder  in  motion.  By 
a  series  of  such  explosions  enough  power  is  developed 
to  run  the  machine.  The  compressed  gas  that  drives 
the  locomotive  is  steam.  The  force  that  compresses  the 
steam  comes  from  the  burning  fuel  which  causes  the 
water  to  evaporate.  Water  is  made  to  evaporate  by 
causing  the  molecules  to  move  so  fast  that  they  will  not 
stay  in  the  liquid.  So  many  of  the  molecules  of  steam 
hit  the  sides  of  the  boiler  that  they  sometimes  have 
a  pressure  of  250  pounds  per  square  inch.  When  the 
engineer  opens  the  valves  the  molecules  rush  through  at 
an  enormous  speed  and  exert  enough  pressure  on  the 
piston  in  the  cylinder  to  turn  the  wheels  of  the  locomotive 
and  thus  move  the  whole  train  of  cars. 

Heat  causes  the  molecules  of  a  gas  to  move  faster  and 
to  strike  the  sides  of  the  containing  vessel  with  greater 
force.  To  apply  heat  to  a  gas,  then,  will  increase  its 
pressure  without  increasing  its  weight  or  density.  If 
the  pressure  on  a  gas  is  not  increased  when  heat  is  ap- 
plied, "the  gas  will  expand  and  become  less  dense.  Bal- 
loons are  sometimes  filled  with  hot  air,  but  they  will 
descend  as  soon  as  the  air  in  them  cools  to  about  the 
temperature  of  the  air  around  them.  Why?  The  air 


SOME  PROPERTIES  OF  GASES  167 

on  the  earth's  surface  is  compressed  by  the  weight  of 
the  miles  of  air  above  us.  When  the  air  is  heated  it 
expands  and  becomes  less  dense,  but  its  pressure  remains 
practically  the  same,  because  the  molecules  move  with 
greater  speed  and  strike  with  greater  force. 

111.  Compression  and  Heat.  —  When  gases  are  heated 
either  their  pressure  or  their  volume  will  increase.  When 
air  is  heated  it  expands,  becomes  less  dense,  and  occupies 
more  space.  If  this  expanded  air  is  compressed,  it  will 
give  out  as  much  heat  as  it  took  up  when  it  expanded. 
(Recall  the  law  of  conservation  of  energy.)  The  fact 
that  air  does  give  out  heat  when  it  is  compressed  has 
been  experienced  by  everyone  who  has  used  a  bicycle 
pump.  After  a  few  strokes  are  made  the  body  of  the 
pump  becomes  warm.  This  heat  is  partially  due  to  the 
friction  of  the  piston  inside,  but  most  of  the  heat  is  due 
to  the  fact  that  the  air  is  being  compressed;  the  molecules 
are  being  forced  into  less  space,  and  they  cannot  move 
so  freely,  so  their  heat  is  given  out.  If  compressed  air  is 
cooled  and  then  allowed  to  expand,  its  temperature  will 
fall  and  will  take  heat  from  surrounding  objects.  Let  the 
escaping  air  of  a  bicycle  tire  touch  your  hand  and  see  how 
cool  it  feels.  When  ammonia  gas  whose  temperature  is 
about  15°  F.  is  compressed  by  a  powerful  engine,  its  tem- 
perature at  once  rises  very  nearly  to  200°  F.  This  increase 
in  temperature  is  not  due  to  the  friction  of  the  com- 
pression pump,  but  it  is  due  to  the  fact  that  the  molecules 
of  ammonia  are  crowded  closer  together  and  the  loss 
of  energy  in  molecular  activity  appears  in  the  form  of 
heat.  If  this  compressed  ammonia  gas  is  permitted  to 
expand  again,  its  temperature  falls  to  what  it  was  at  first. 
In  general,  when  gases  are  compressed,  they  give  out  heat, 
and  when  they  are  allowed  to  expand  they  take  up  heat. 


i68 


GENERAL  SCIENCE 


112.  Refrigeration.  —  From  the  facts  in  §  1 1 1 ,  we 
can  easily  understand  that  gases  can  be  used  for  cooling 
purposes.  When  fruits  and  vegetables  are  placed  in 
cold  storage  a  freezing  temperature  is  not  desired,  so  air 
can  be  used  to  keep  the  building  cool.  The  air  is  com- 
pressed and  forced  through  metal  pipes  with  water  run- 
ning over  them  to  cool  the  condensed  air.  This  air  is 
then  allowed  to  escape  in  the  storage  rooms,  which  are 
thus  kept  at  a  low  temperature. 


AMMONIA  CONDENSING  PIPES  ON  THE  ROOF  OF  AN  ICE  PLANT 


Liquids,  when  tiiey  evaporate,  take  up  a  great  amount 
of  heat;  this  we  know  from  our  experience  with  water. 
To  experience  the  cooling  effect  of  evaporating  liquids, 
place  a  few  drops  of  the  following  compounds  on  the  back 
of  your  hand  in  the  order  named:  —  ether,  alcohol, 
ammonia,  and  water.  The  one  that  evaporates  the  fast- 
est will  feel  the  coolest,  because  the  faster  the  molecules 


SOME  PROPERTIES  OF  GASES  169 

leave  your  hand  the  more  heat  is  required  to  supply  the 
energy  necessary  for  them  to  fly  away. 

The  compound  that  is  used  for  refrigeration  by  evapo- 
ration is  ammonia,  (NH3).  Ammonia  at  ordinary  pres- 
sure and  temperature  is  a  gas.  At  —  40°  C.  it  condenses 
and  forms  a  liquid,  or  it  can  be  made  to  liquefy  at  a 
higher  temperature  if  the  pressure  is  increased.  The 
ammonia  is  purchased  in  liquid  form  in  long  cylindrical 
tanks.  The  cold-storage  buildings  in  which  ammonia 
is  used  have  a  system  of  closed  iron  pipes,  compression 
pumps,  and  a  place  to  liquefy  the  ammonia  by  cooling 
it  after  it  is  compressed  by  the  pumps.  The  ammonia 
is  put  into  this  system  of  pipes,  from  which  it  cannot 
escape.  It  is  made  to  circulate  by  the  pumps.  The 
pumps  compress  the  ammonia  gas  and  it  is  then  cooled 
and  liquefied  while  passing  through  pipes  over  which  cool 
water  is  kept  flowing.  The  cooling  pipes  are  usually  in 
the  open  air,  often  on  top  of  the  building.  After  the 
ammonia  is  liquefied,  it  flows  to  the  cold-storage  rooms, 
where  it  is  permitted  to  pass  slowly  through  valves,  and 
then  it  evaporates  rapidly  because  the  pumps  draw  off 
the  ammonia  gas  as  fast  as  it  is  formed  by  evaporation. 
The  evaporating  ammonia  takes  the  heat  from  the  pipes 
in  which  it  is  enclosed  and  the  pipes  in  turn  take  heat 
from  the  air  in  the  room,  which  is  thus  kept  at  a  very 
low  temperature,  even  below  freezing  if  desired.  Large 
meat-packing  firms  and  sometimes  small  meat-markets  use 
ammonia  for  refrigeration.  Ice  is  also  used  for  refrigera- 
tion, especially  in  refrigerator  cars  and  in  private  houses. 

113.  Artificial  Ice.  —  Ice  in  the  summer  used  to  be 
regarded  as  a  luxury,  but  now  it  is  a  necessity;  without 
the  modern  methods  of  making  ice,  it  would  be  very 
expensive.  Boards  of  health  require  artificial  ice  to  be 


170 


GENERAL  SCIENCE 


made  of  distilled  water,  and  for  this  reason  it  is  purer 
and  more  free  from  germs  than  the  ice  of  rivers  or 
lakes. 

The  water  to  be  frozen  is  put  into  a  metal  tank  that 
holds   about   300  pounds,  as  shown  in   the  illustration. 


DRAWING  3oo-PouND  CANS  or  ICE  FROM  THE  SALT  WATER 

These  tanks  are  usually  about  four  feet  high  and  they 
are  lowered  into  a  large  tank  of  salt  water,  which 
generally  covers  as  much  area  as  a  large  room,  but  not 
deep  enough  to  permit  the  salt  water  to  flow  into 
the  freshwater  tanks.  The  temperature  of  the  salt 
water  is  kept  at  about  14°  F.  or  -10°  C.  (A  saturated 
solution  of  salt  water  freezes  at  -22°  C.)  The  tempera- 
ture of  the  salt  water  is  kept  low  by  ammonia  pipes  which 
are  in  the  salt  water  between  the  rows  of  freshwater 
tanks.  The  ammonia  here  goes  through  the  same  pro- 
cess as  that  described  in  §  112  on  refrigeration  with 


SOME  OF  PROPERTIES   GASES  171 

ammonia.     It  requires  about  36  hours  for  the  300  pounds 
of  water  to  freeze  into  a  solid  piece  of  ice. 

114.  Liquid  Air.  —  Steam  is  a  gas  and  can  be  liquefied 
by  subjecting  it  to  great  pressure  or  by  cooling  it.     Am- 
monia (NH3)  under  ordinary  conditions  is  a  gas,  and  it 
can  be  liquefied  by  cooling  or  by  adding  pressure.     It 
can  be   more   easily  liquefied  by  both  cooling   and  in- 
creasing the  pressure.     By  cooling  a  gas  the  molecules 
become  less  active  and  by  using  pressure  they  can  be 
forced   closer   together.     If   the   cooling  and  increase  of 
pressure  are  continued  far  enough,  the  molecules  become 
so  inactive  and  so  close  together  that  the  force  of  attrac- 
tion which  they  have  for  one  another  overpowers  their 
force  of  free  motion.     When  molecules  are  in  this  condi- 
tion we  have  what  is  usually  called  a  liquid.     (In  some 
cases  it  would  be  a  solid.)     Then,  in  order  to  make  a 
liquid  of  any  gas  all  that  needs  to  be  done  is  to  lower 
the  temperature  of  the  gas  and  increase  the  pressure  on 
it.     Air,  oxygen,  and  hydrogen  can  be  liquefied  in  this 
way.     Under  average  air  pressure,  liquid  air  will  boil  on 
ice.     In   1900   a   temperature  of  -260°  C.,   or  -436°  F., 
was  produced  by  Professor  James  Dewar,  by  evaporat- 
ing liquid  hydrogen  in  a  partial  vacuum. 

115.  Natural  and  Artificial  Gas.  —  During  the  millions 
of  years  while  the  earth's  present  crust  was  in  process  of 
formation,  great  quantities  of  plant  and  animal  matter 
were  buried  beneath  the  surface.     We  now  remove  much 
of  this  material  in  the  form  of  coal,  petroleum,  and  gas. 
This  gas  is  taken  out  of  the  earth  by  drilling  wells,  from 
which  it  is  allowed  to  flow  through  pipes  to  the  storage 
tanks  of  cities.     From  these  tanks  the  gas  is  piped  to 
houses  for  heating,  cooking,  and  lighting. 

Artificial  gas  is  made  by  heating  wood  or  coal  in  ovens 


172 


GENERAL  SCIENCE 


made  for  the  purpose;  no  air  can  get  into  the  ovens. 
The  gas  that  comes  from  the  heated  coal  is  forced  through 
water  and  various  substances  which  remove  all  the  solid 
matter  and  other  undesirable  elements.  The  pure  gas  is 
then  forced  into  storage  tanks  from  which  it  is  piped  to 
buildings  for  the  same  uses  as  natural  gas. 

George  Westinghouse  invented  a  convenient  device 
for  measuring  the  gas  as  each  customer  burns  it.  This 
operates  much  like  the  apparatus  in  the  steam  chest  and 
cylinder  on  an  engine.  The  gas  meter  is  composed  of  a 
metal  case  divided  into  two  parts  by  a  movable  dia- 
phragm, and  a  clockwork  device  records  the  move- 
ments of  this  diaphragm.  When  the  gas  flows  into  one 
side  of  the  meter  the  diaphragm  is  forced  over  and  the 
gas  on  the  other  side  is  forced  out  to  the  burners;  when 
one  side  of  the  meter  is  full  of  gas  the  entrance  valve 
closes  and  the  entrance  valve  of  the  other  side  opens, 
and  through  this  the  gas  enters  and  forces  the  diaphragm 

to  the  opposite  side  and 
the  gas  of  that  side  flows 
out  to  the  burners. 
The  movements  of  the 
diaphragm  are  recorded 
by  the  dials  on  the  gas 
meter. 

Gas  is  measured  by 
the  cubic  foot  and  is 
paid  for  by  the  thousand 
cubic  feet.  Every  person  who  uses  gas  should  know  how 
to  read  a  meter.  A  meter  with  four  dials  will  give  four 
digits,  to  the  right  of  which  we  add  two  ciphers,  thus, 
263,800.  (Provided  the  four  dials  are  all  in  a  row.) 
To  read  one  of  the  dials  we  take  the  smaller  of  the 


INDEX  OF  A  GAS  METER 


SOME  PROPERTIES  OF  GASES  173 

two  digits  on  either  side  of  the  hand  of  that  dial.  We 
begin  with  the  dial  on  the  left  and  read  toward  the  right, 
writing  only  one  digit  for  each  dial.  The  numbers  over 
the  dials  mean  that  when  the  hand  passes  once  around 
the  dial  you  will  have  used  as  many  feet  of  gas  as  the 
number  over  the  dial  indicates.  If  the  number  over 
a  dial  is  "10  thousand,"  the  hand  on  that  dial  will  measure 
10,000  feet  every  time  it  goes  once  around,  and  as  it 
passes  from  one  digit  to  another  it  measures  1,000  feet. 
Read  the  gas  meter  in  the  illustration. 

QUESTIONS    AND    EXERCISES 

1.  Explain  how  gases  produce  pressure. 

2.  If  we  increase  the  pressure  on  confined  gas,  how  will  its 
volume  be  affected  ? 

3.  The  pressure  in  an  automobile  tire  in  a  cool  garage  is  70 
pounds;  how  will  the  pressure  be  affected  if  the  automobile  is 
placed  in  the  hot  sunshine  ? 

4.  Why  does  the  air  escaping  from  a  bicycle  or  automobile 
tire  feel  cool? 

5.  What  practical  use  is  made  of  the  fact  that  gases  take  up 
heat  when  they  are  allowed  to  expand  ? 

6.  Visit  some  artificial  ice-plant  and  explain  the  process  used. 

7.  Give  the  origin  of  natural  gas.     How  is  artificial  gas  made  ? 

8.  Draw  the  dials  and  hands  of  your  gas  meter  several  days  in 
succession,  also  record  the  number  of  cubic  feet.     Do  the  same 
for  the  electric  meter.     (Continue  this  until  you  know  how  to 
read  both  of  them.) 


CHAPTER  XIX 
SIMPLE   MACHINES 

116.  Evolution  of  Machines.  —  Primitive  man,  who 
spent  most  of  his  time  gathering  food  from  the  plants 
that  grew  wild  and  by  killing  wild  animals,  did  not  know 
much  about  even  the  simplest  machines,  and  he  had  but 
little  use  for  them.  The  first  tool  that  he  learned  to  use 
was  the  stone  or  club  which  he  chanced  to  hurl  at  an 
animal  for  self-protection  or  to  secure  the  animal  for 
food.  Later  he  learned  how  to  make  a  sling  of  a  piece  of 
hide,  with  which  a  stone  could  be  thrown  with  greater 
force,  and  by  practice  accuracy  was  developed.  This 
device  was  the  first  machine  which  man  used  to  subdue 
nature,  and  he  has  been  busy  conquering  the  forces  of 
nature  ever  since.  Probably  the  next  machine  which 
man  used  in  the  pursuit  of  game  was  the  lever,  by  taking 
a  stick  to  pry  open  a  log  or  to  remove  a  stone  from  a 
hole  into  which  an  animal  had  fled  for  protection.  Next 
came  a  cutting  device  made  of  a  sharp  bone  or  stone. 

After  primitive  man  had  learned  to  use  these  three 
simple  devices,  —  the  sling,  lever,  and  crude  knife,  — •  he 
was  well  on  the  road  toward  civilization.  They  gave  him 
something  to  think  about.  The  thinking  led  to  wider 
uses  and  modifications  of  the  simple  machines.  He 
could  now  build  a  place  in  which  to  live  and  protect 
himself  from  his  enemies.  To  live  in  one  locality  required 
man  to  store  food  when  it  was  plentiful  in  order  to  nour- 
ish himself  in  time  of  scarcity.  By  combining  the  lever 


SIMPLE   MACHINES  175 

and  cutting  tool,  he  made  a  machine  with  which  he  could 
dig  up  the  soil  and  make  it  more  favorable  for  the  growth 
of  plants.  This  was  primitive  agriculture.  He  also 
learned  to  befriend  certain  animals  and  to  protect  them 
with  his  weapons.  Thus  began  primitive  stock-raising 
and  the  use  of  animals  as  beasts  of  burden. 

Then  came  a  comparatively  rapid  development  of 
machines  for  clearing  the  trees  and  stones  from  the 
fields,  for  transporting  some  of  the  trees  and  stones  for 
building  purposes,  for  erecting  larger  buildings,  and  in 
comparatively  recent  times  for  manufacturing  and  ex- 
tensive transportation.  But  we  must  not  lose  sight  of 
the  fact  that  the  simple  devices  and  tools  used  by  primi- 
tive man  are  still  used  by  the  most  highly  civilized  people, 
but  with  modifications,  improvements,  and  almost  an 
infinite  number  of  additional  machines  of  all  kinds. 
The  people  of  today  have  the  enormous  heritage  of  all  the 
mechanical  devices  ever  thought  of  by  man  from  primitive 
times  to  modern. 

If  the  leading  races  of  mankind  had  depended  only 
upon  their  physical  strength  to  subdue  and  conquer 
nature,  instead  of  seeking  to  invent  new  devices  and 
to  discover  new  methods  of  obtaining  food  and  shelter, 
the  world  today  would  be  in  the  condition  that  is  preva- 
lent in  the  wild  parts  of  Asia,  Africa,  and  South  America, 
where  the  natives  still  use  only  the  crudest  tools  and 
implements  of  primitive  man. 

We  sometimes  wonder  how  people  a  few  hundred 
years  ago  could  live  at  all,  when  we  think  of  the  enormous 
amount  of  complex  machinery  in  use  today,  transport- 
ing man  from  place  to  place  and  bringing  him  food  and 
clothing  from  the  most  distant  parts  of  the  earth.  The 
steamboat,  railroad,  telegraph,  sewing  machine,  harvest- 


i76  GENERAL  SCIENCE 

ing  machine,  street  car,  telephone,  all  came  into  use 
during  the  past  century.  Without  modern  machinery 
it  would  not  be  possible  to  take  coal,  petroleum,  and  gas 
from  the  earth.  To  the  scientists,  the  thinkers,  whb 
brought  all  these  modern  mechanical  devices  into  exist- 
ence, the  world  owes  a  debt  which  it  never  can  pay. 

117.  Definitions.  —  In  order  to  understand  the  princi- 
ples of  some  of  the  simple  machines,  it  is  necessary  to 
get  a  definite  idea  of  a  few  words  which  are  used  in 
discussing  them. 

(A)  Energy.  —  In  the  chapters  on  heat  we  often  used 
the  word  energy,  and  we  have  some  idea  of  its  meaning. 
Coal  and  wood  have  energy  which  can  be  changed  into 
heat  by  oxidation.  Hot  iron  has  more  energy  than 
cold  iron,  and  this  energy  can  be  removed  from  the  iron 
by  plunging  it  into  cold  water.  The  water  then  has  the 
energy  which  the  iron  had.  These  objects  have  energy 
by  virtue  of  their  condition. 

We  also  have  energy  in  our  bodies  and  can  use  it  at 
will.  A  boy  coasting  down  a  hill  on  a  bicycle  has  enough 
energy  to  coast  part  way  up  another  hill.  A  stone  thrown 
into  the  water  makes  the  water  splash  and  wave,  because 
of  its  energy.  The  energy  of  a  falling  hammer  will  drive 
a  stake  into  the  ground.  These  objects  have  energy  because 
of  their  motion. 

A  boy  on  a  sled  on  the  top  of  a  hill  in  winter  has  enough 
energy  to  take  him  to  the  bottom.  A  book  held  above 
the  desk  has  sufficient  energy,  if  permitted  to  fall,  to 
shake  the  desk.  Water  in  a  city  reservoir  has  enough 
energy  to  cause  it  to  flow  through  the  pipes  to  the  houses. 
These  things  have  energy  because  of  their  position. 

So  objects  may  have  energy  by  virtue  of  their  condi- 
tion, motion,  or  position.  Energy  which  is  due  to  the 


SIMPLE   MACHINES  177 

condition  or  position  of  an  object  is  called  potential 
energy.  Energy  of  an  object  which  is  due  to  motion  is 
called  kinetic  energy.  Energy  is  ability  or  capacity  to 
move  an  object.  To  walk  requires  energy  because  our 
body  is  the  object  moved.  It  requires  energy  to  move 
a  wagon,  a  car,  or  a  train.  Energy,  like  heat,  cannot  be 
thought  of  apart  from  some  object  or  substance. 

(B)  Force.  —  We   never   use   at   one   time   all   of   the 
energy  stored  in  our  body,  but  only  a  part  of  it  at  one 
time.     When  we  walk,  throw  a  ball,  turn  a  machine,  or 
lift   a  book   we   use   part   of    the   energy   of   our   body. 
The    part    of    the    energy    that    we    use    at    any    one 
time  is  called  force.     So  force  is  the  amount  of  effort 
exerted  at  any  one  time.     Or,  force  is  the  energy  which 
is  in  process  of  use ;  or,  force  is  the  energy  which  is  being 
used  to  move  or  hold  an  object.     Force,  then,  like  energy, 
cannot  be  thought  of  apart  from  matter  or  objects. 

To  hold  in  the  hand  an  iron  ball  which  weighs  a  pound 
requires  us  to  exert  a  "pound  of  force."  A  pound  of 
force  is  the  force  exerted  by  the  earth  on  a  pound  of  mass 
or  matter  in  pulling  the  matter  toward  its  center.  The 
earth's  force  or  "pull"  on  an  object  is  called  gravity. 
To  hold  in  the  hand  a  ball  which  weighs  a  gram  requires 
one  to  exert  a  "gram  of  force."  The  pound  of  force  and 
the  gram  of  force  are  two  units  of  force.  There  is  no 
unit  of  energy  because  we  do  not  measure  energy  except 
when  it  appears  in  the  for,m  of  force  or  heat,  and  then 
we  call  it  force  or  heat  respectively. 

(C)  Work.  —  If  a  2oo-pound  force  is  exerted  upon  a 
barrel  weighing  400  pounds,  no  work  is  done  if  the  barrel 
does  not  move.     Holding  a  book  in  one  place  is  not 
working.     In  these  instances  force  is  used,  but  no  work 
is  done.     Picking  up  a  book  from  the  floor  and  placing 


iy8  GENERAL  SCIENCE 

it  on  the  desk  is  work.  Carrying  bricks  or  mortar  up  a 
ladder  is  work.  We  do  work  when  we  lift  a  2oo-pound 
box  into  a  wagon.  We  do  four  times  as  much  work  when 
we  lift  a  4oo-pound  box  into  a  wagon  as  when  we  lift  a 
loo-pound  box  into  the  same  wagon.  We  do  four  times 
as  much  work  when  we  lift  a  loo-pound  box  up  four  feet 
as  when  we  lift  the  same  box  up  one  foot. 

From  these  statements  we  see  that  to  do  work  it  is 
necessary  that  the  object  be  moved,  that  is,  work  is  a 
result  and  not  an  effort.  Work  is  a  result  of  force  and 
not  force  itself.  The  amount  of  work  done  depends 
upon  the  amount  of  the  force  and  the  distance  through 
which  the  object  is  moved.  To  move  a  given  object 
ten  feet  requires  twice  as  much  work  as  to  move  the  same 
object  five  feet,  but  the  force  required  is  the  sanie  in  each 
case.  Twice  as  much  work  is  done  when  a  loo-pound 
object  is  lifted  four  feet  as  when  a  5o-pound  object  is  lifted 
four  feet;  here  the  distances  are  the  same  but  the  forces 
are  different. 

Work  is  the  result  of  a  force  moving  through  a  distance. 
Or,  work  =  force  multiplied  by  the  distance  the  force 
moved ;  or,  W  =  f  X  d  (w=  work,  /  =  force,  d  =  distance.) 

118.  Unit  of  Work.  —  Since  force  and  distance  can 
be  measured,  work  also  can  be  measured.  The  unit  of 
work  in  the  English  system  is  the  foot  pound.  The 
foot  pound  is  the  work  done  when  a  " pound  of  force'' 
moves  through  a  distance  of  one  foot.  If  we  lift  one 
pound  up  one  foot,  we  do  a  foot  pound  of  work.  To 
lift  10  pounds  five  feet  we  do  50  foot  pounds  of  work. 
If  a  boy  weighing  100  pounds  climbs  a  ladder  10  feet 
high,  he  does  1,000  foot  pounds  of  work.1 

1  In  the  metric  system  a  unit  of  work  is  the  gram  centimeter.  The 
gram  centimeter  is  the  work  done  when  a  "gram  of  force"  moves  through 


SIMPLE  MACHINES  179 

119.  A   Machine   is   a   device   used   to    transform   or 
transfer  energy  and  to  apply  force  for  doing  useful  work. 
Illustration   of   how   a   machine   can   transform   energy: 
when  coal  is  burned  in  the  fire-box  of  a  boiler,  the  heat 
of  the  coal  makes  steam  of  the  water,  and  the  steam  in 
running  the  engine  develops  mechanical  energy,  which 
can  be  made  to  develop  electricity  or  electrical  energy 
by   turning   a   dynamo.     The   electrical   energy   can   be 
changed  back  to  mechanical  energy  and  drive  street  cars 
along  the  tracks.     All  kinds  of  steam  and  gas  engines  and 
electrical  machines  are  devices  for  transforming  energy  as 
well  as  for  transferring  it;  while  the  simple  machines  are 
either  devices  for  transferring  energy  or  devices  to  which 
force  can  be  applied  and  useful  work-  result. 

The  simple  machines  are  six  in  number:  The  (i)  lever, 
(2)  inclined  plane,  (3)  wedge,  (4)  screw,  (5)  pulley,  and 
(6)  wheel  and  axle.  Of  these  the  lever  and  inclined  plane 
are  basic  types.  The  pulley  and  the  wheel  and  axle  are 
modified  forms  of  the  lever,  while  the  wedge  and  screw 
are  modified  inclined  planes.  All  complex  machines  are 
only  combinations  of  two  or  more  simple  machines. 

120.  The  Mechanical  Advantage  of  a  machine  is  the  ratio 
of  the  resistance  (as,  for  instance,  the  weight  lifted)  to  the 
force  applied.     The  weight  in  pounds  divided  by  the  force 
in  pounds  gives  the  mechanical  advantage.    The  mechanical 
advantage  of  a  machine  is  also  the  ratio  of  the  distance 
that  the  force  moves  to  the  distance  that  the  resistance 
moves.     That  is,  force  distance  divided  by  weight  distance 

a  distance  of  one  centimeter.  If  we  lift  a  gram  one  centimeter,  we  do  a 
gram  centimeter  of  work.  The  smallest  unit  of  work  in  the  metric  system 
is  the  erg.  The  gram  centimeter  is  equal  to  980  ergs.  (An  erg  is  the 
work  done  by  a  force  of  one  dyne  moving  through  a  distance  of  one  centi- 
meter. A  dyne  is  a  force  that  can  give  to  a  gram  mass  an  increase  in 
speed  of  one  centimeter  per  second.) 


i8o  GENERAL  SCIENCE 

is  the  mechanical  advantage.  (The  above  statements  do 
not  take  into  consideration  the  loss  by  friction.)  For 
instance,  if  by  the  use  of  a  machine  a  5oo-pound  piano  is 
lifted  10  feet  by  a  force  of  100  pounds  moving  50  feet,  the 
.  mechanical  advantage  of  this  machine  is  500  pounds  di- 
vided by  100  pounds  or  5.  Again,  the  mechanical  advan- 
tage is  50  feet  -f-  10  feet  =5.  (Friction  not  considered.) 
121.  Efficiency.  —  Machines,  especially  the  simple 
machines,  are  often  thought  of  as  devices  for  saving 
work.  If  a  heavy  object  that  could  not  be  moved  with- 
out a  machine  can  be  moved  by  the  use  of  one,  we  are 
willing  to  waste  a  little  work  to  accomplish  our  purpose. 
By  the  use  of  a  machine  the  force  applied  does  not  have 
to  be  so  great  as  it  would  have  to  be  without  the  machine, 
but  the  force  has  to  move  much  farther  than  the  weight 
lifted  to  accomplish  the  desired  result.  Hence  the  work 
put  into  a  machine  is  always  equal  to  or  greater  than  the 
work  got  out  of  the  machine.  Work  =  force  X  distance, 
so  the  work  put  into  a  machine  will  be  the  force  X  the 
force  distance,  and  the  work  got  out  of  a  machine  will  be 
the  weight  X  the  weight  distance.  The  work  got  out  of  a 
machine  will  be  less  than  the  work  put  into  it,  if  there  is 
any  loss  by  friction.  All  machines  have  more  or  less  fric- 
tion; when  friction  resists  man's  force  in  machines  the  ef- 
ficiency of  the  machine  is  less  than  one,  but  if  friction  is 
assisting  in  mechanical  work  the  efficiency  is  greater  than 
one.  The  efficiency  of  a  machine  is  the  ratio  of  the  work 
done  by  the  machine  to  the  work  spent  on  the  machine. 

Work  accomplished 

Efficiency  —  - 

Work  spent 

Efficiency  is  expressed  in  per  cent;   90  per  cent  efficiency 
means  that  one  part  of  the  work  spent  on  a  machine  is 


SIMPLE   MACHINES 


181 


wasted  by  friction  and  nine  parts  results  in  useful  work. 
When  an  object  is  lowered  by  a  machine,  the  efficiency 
of  the  machine  is  usually  more  than  100  per  cent,  because 
friction  is  resulting  in  useful  work  by  helping  to  keep 
the  object  from  descending  too  fast.  Friction  is  useful 
in  checking  the  speed  of  street  cars  and  trains  going 
down  long  grades  and  also  for  stopping  them. 

122.  The  Lever.  —  The  lever  is  a  rod  free  to  turn  about 
a  point.  The  fulcrum  is  the  point  around  which  the 
lever  turns.  A  seesaw  is  one  kind  of  a  lever:  if  the  two 
persons  on  it  are  of  equal  weight,  they  take  positions 
which  are  the  same  distance  from  the  point  about 
which  the  seesaw  turns.  If  two  persons  of  unequal 
weight  get  on  a  seesaw,  the  one  who  is  the  heavier  will 
take  a  position  closer  to  the  fulcrum  than  the  one  of  less 
weight.  If  a  person  whose  weight  is  100  pounds  takes 
a  position  6  feet  from  the  fulcrum  and  a  person  whose 
weight  is  75  pounds  takes  a  position  8  feet  from  the 
fulcrum,  they  will  balance  on  the  seesaw.  The  reason 
that  they  will  balance  is  because  100  X  6  is  equal  to 


0         4|0         3|0        2|0         HO 


LEVER  OF  THE  FIRST  CLASS 

75  X  8.  If  a  person  weighing  50  pounds  is  10  feet  from 
the  fulcrum  and  a  person  weighing  100  pounds  is  5  feet 
from  the  fulcrum,  they  will  balance,  because  50  X  10  is 
equal  to  100  X  5. 

Balance  a  meter  stick  as  shown  in  the  illustration,  and 


182  GENERAL  SCIENCE 

let  a  mass  of  200  grams  be  hung  by  a  thread  from  a  point 
30  cm.  from  the  fulcrum.  Then  let  a  point  be  found  on 
the  opposite  side  of  the  fulcrum  at  which  a  weight  of  150 
grams  will  just  balance  the  200  grams  This  point  will 
be  found  to  be  40  cm.  from  the  fulcrum.  We  see  the 
reason  at  once,  because  the  product  of  200  X  30  is  equal 
to  the  product  of  150  X  40. 

The  seesaw  and  the  meter  stick,  when  used  as  described 
above,  are  levers.  The  important  things  to  keep  in  mind 
about  a  lever  are:  (i)  the  large  weight,  which  may  be 
called  the  resisting  force;  (2)  the  small  weight,  which  may 
be  called  the  acting  force;  (3)  the  fulcrum,  about  which  the 
lever  turns;  (4)  the  distance  from  the  fulcrum  to  the  weight, 
which  is  called  the  weight  arm;  and  (5)  the  distance  from 
the  fulcrum  to  the  force,  which  is  called  the  force  arm. 

The  law  of  levers  is:  The  force  multiplied  by  the  length 
of  the  force  arm  is  equal  to  the  weight  multiplied  by  the 
length  of  the  weight  arm. 

Force  X  force  arm  =  weight  X  weight  arm. 
For  instance,  10  g.  with  a  force  arm  of  10  cm.  will  balance 
25  g.  with  a  weight  arm  of  4  cm:  10  X  10  =  25  X  4. 
That  is,  the  moment  of  the  acting  force  is  equal  to  the 
moment  of  the  resisting  force.  The  moment  of  a  force  is 
that  which  is  trying  to  produce  rotation  around  a  point. 
When  the  two  opposing  moments  are  equal  there  will  be 
no  motion  and  the  lever  will  balance. 

The  mechanical  advantage  of  a  lever  is  (i)  the  ratio  of 
the  weight  to  the  force,  or  (2)  the  ratio  of  the  force  arm 
to  the  weight  arm,  or  (3)  the  ratio  of  the  distance  the 
force  moves  to  the  distance  the  weight  is  moved. 
d)  (2)  (3) 

W       F.  arm        F.  distance  ,      .    ,     , 

-  =  -          -  =  -  -  =  mechanical  advantage. 

F       W.  arm       W.  distance 


SIMPLE   MACHINES  183 

From  the  lever  described  on  the  opposite  page, 

25  g       io  cm  .       • 

—  =  2.5  =  mechanical  advantage. 
10  g        4  cm 

F.  distance  is  the  distance  the  force  moved,  and  W. 
distance  is  the  distance  the  weight  moved.  The  force 
multiplied  by  the  force  distance  (the  work  spent  on  the 
lever)  is  equal  to  the  weight  multiplied  by  the  weight 
distance  (the  work  accomplished  by  use  of  the  lever). 
It  is  evident  from  this  that  the  lever  is  not  a  machine  to 
save  work,  but  it  is  a  device  by  which  a  large  weight  can 
be  moved  by  a  small  force,  but  the  force  must  move  a 
much  greater  distance  than  that  through  which  the  weight 
lifted  moves.  For  example,  we  can  lift  a  4oo-pound 
stone  by  a  force  of  100  pounds  if  we  place  one  end  of  a 
lever  under  the  stone  and  then  place  a  block  of  wood  or 
a  small  stone  under  the  lever  for  a  fulcrum,  and  then 
apply  to  the  lever  a  force  of  100  pounds  at  a  point  on 
the  lever  four  times  as  far  from  the  fulcrum  as  the  fulcrum 
is  from  the  weight.  If  the  force  arm  is  eight  feet  and 
the  weight  arm  is  two  feet,  the  force  will  move  four  times 
as  fast  as  the  weight,  and  the  force  will  move'  four  feet 
while  the  stone  moves  one  foot.  The  work  done  on  the 
stone  will  be  400  pounds  X  i  foot,  or  400  foot  pounds. 


LEVERS  or  THE  FIRST  CLASS 


123.  Classes  of  Levers.  —  Since  there  are  three  im- 
portant positions  on  the  lever,  namely,  the  fulcrum,  the 
position  of  the  force,  and  the  position  of  the  weight, 
levers  are  divided  into  three  classes  according  to  the 


1  84  GENERAL  SCIENCE 

position  of  the  fulcrum  with  respect  to  the  force  and 
weight. 

(a)  The  lever  of  the  first  class  is  one  with  the  fulcrum 
between  the  force  and  the  weight.  Examples  of  this 
class  are:  common  steelyards,  scissors,  the  balancing  arm 
of  platform  scales,  most  pump  handles,  and  a  crowbar 
when  it  is  shoved  under  an  object,  a  fulcrum  put  under 
and  the  force  end  shoved  downward,  thus  lifting  the 
object  upward. 

rm  _  t 


LEVERS  or  THE  SECOND  CLASS 

(5)  The  lever  of  the  second  class  is  one  with  the  weight 
between  the  force  and  the  fulcrum.  Examples  of  this 
class  are:  the  nut-cracker  with  the  fulcrum  at  the  hinge, 
the  force  at  the  handle  (the  weight  is  the  pressure  put  on 
the  nut  to  crack  it);  the  wheelbarrow  with  the  fulcrum 
at  the  axle  of  the  wheel  and  the  force  at  the  handles; 
the  foot  when  we  stand  on  the  toes,  which  form  the  ful- 
crum, the  weight  being  on  the  ankle  joint,  and  the  force 
applied  at  the  heel.  In  the  lever  of  the  second  class  the 
force  arm  is  the  entire  lever-bar;  the  fulcrum  is  at  one 
end  and  the  force  at  the  other.  The  force  arm  is  the 
distance  from  the  force  to  the  fulcrum.  The  weight 
arm  is  the  distance  from  the  weight  to  the  fulcrum.  A 
bar  10  feet  long  will  give  a  higher  mechanical  advantage 
if  it  is  used  as  a  lever  of  the  second  class  than  if  it  is 
used  as  a  lever  of  the  first  class. 

(c)  The  lever  of  the  third  class  is  one  with  the  force 
between  the  weight  and  the  fulcrum.  Examples  of  this 
class  are:  the  pitchfork  with  the  weight  on  the  end,  the 


SIMPLE   MACHINES  185 

left  hand  on  the  other  end,  which  is  the  fulcrum,  and 
the  right  hand  between,  which  is  the  force;  (if  the  left 
hand  pushes  downward  and  the  right  hand  holds  its 


fl 

LEVER  OF  THE  THIRD  CLASS 

position  the  pitchfork  is  a  lever  of  the  first  class);  the 
forearm  with  the  fulcrum  at  the  elbow,  the  weight  on 
the  hand,  and  the  force  applied  just  below  the  elbow 
joint;  the  whole  arm  with  the  fulcrum  at  the  shoulder 
joint.  In  the  lever  of  the  third  class  the  weight  arm  is 
the  entire  lever  bar.  The  weight  arm  is  the  distance 
from  the  weight  to  the  fulcrum.  The  mechanical  ad- 
vantage of  the  lever  of  the  third  class  is  less  than  one; 
the  force  is  greater  than  the  weight  lifted.  It  is  used  to 
move  small  objects  rapidly  and  with  high  speed,  while  the 
levers  of  the  first  and  second  class  are  used  to  move 
heavy  objects  with  a  small  force.  The  bones  of  the 
body  are  used  as  levers  of  the  third  class,  with  the  ful- 
crum at  the  joints,  and  powerful  muscles  with  their 
tendons  attached  just  across  the  joints  act  as  forces  to 
move  the  parts  of  the  body  with  rapidity. 

The  lever  of  the  first  class  can  also  be  used  for  speed 
and  for  throwing  objects,  if  the  force  arm  is  made  short 
and  the  weight  arm  made  long.  This  would  require  a 
large  force  to  lift  a  small  weight  and  the  mechanical  ad- 
vantage would  be  less  than  one. 

Problems.  1.  In  which  of  the  three  classes  of  levers  do  the 
following  belong:  a  boat  oar,  grocer's  scales,  sugar  tongs,  a  claw 
hammer,  and  a  hatchet  pulling  a  nail? 

2.  How  would  you  arrange  a  ruler  to  use  it  as  a  lever  of  the  first 
class,  and  then  as  a  lever  of  the  second  class,  in  lifting  a  book? 

3.  If  a  lever  of  the  second  class  is  10  feet  long,  what  is  the  median- 


i86  GENERAL  SCIENCE 

ical  advantage  if  the  weight  is  2  feet  from  the  fulcrum?  How  large 
could  the  weight  be  if  a  force  of  100  pounds  would  just  lift  it? 

4.  If  a  lever  of  the  first  class  is  10  feet  long,  and  the  fulcrum  is 
2  feet  from  the  end,  what  is  the  mechanical  advantage?  How 
much  force  will  be  required  to  lift  a  weight  of  600  pounds? 

6.  A  lever  of  the  third  class  is  10  feet  long,  with  the  force  2  feet 
from  the  fulcrum.  What  force  is  required  to  lift  a  weight  of  10 
pounds?  What  is  its  mechanical  advantage? 

124.  The  Inclined  Plane. — The  inclined  plane  is  a 
simple  device,  often  composed  of  one  or  more  planks 
elevated  at  one  end,  so  that  objects  may  be  rolled  up 
or  down.  In  order  to  understand  the  principle  of  the 
inclined  plane,  let  us  recall  some  of  our  experiences.  We 
know  that  we  become  tired  more  quickly  walking  up  a 
grade  than  while  walking  on  the  level,  and  the  steeper 
the  grade  the  more  force  it  takes  to  ascend  it.  It  is 
harder  to  ride  a  bicycle  up  a  steep  grade  than  to  ride  up 
a  very  gradual  grade.  The  hill  that  is  hard  to  climb  in 
winter  is  the  one  down  which  we  can  coast  the  fastest. 
We  can  see  from  our  own  experiences  that  the  slope  of 
the  plane  is  what  determines  the  force  required  to  roll 

^-  an  object  up  it,  and 
F    the   length  of  the 
plane  determines  the 
amount  of  work  done 


while  rolling  an  ob- 
ject up  it. 

To  test  our  obser- 
vations let  us  try  an 
INCLINED  PLANE 

experiment    with   a 

plane,  a  rolling  weight,  and  a  spring  balance.  In  the  illus- 
tration, the  length  of  the  plane  is  AB,  the  height  is  BC,  the 
weight  moving  up  is  W,  and  the  force  moving  it  is  F, 
measured  by  the  spring  balance.  If  the  height  BC  is 


SIMPLE   MACHINES  187 

one-half  the  length  AB,  the  force  F  is  one-half  the 
weight  W.  If  the  height  BC  is  one-fourth  the  length 
AB,  then  the  force  F  is  one-fourth  the  weight  W. 
Now  let  BC  be  4  feet,  the  length  AB  be  8  feet,  and 
the  weight  be  400  pounds;  then  the  force  will  be  200 
pounds,  because  the  force  multiplied  by  the  force  dis- 
tance equals  the  weight  multiplied  by  the  weight  dis- 
tance: (200  X  8  =  400  X  4).  If  BC  is  2  feet,  AB  is  8 
feet,  the  weight  is  400  pounds,  and  the  force  is  100 
pounds:  100  X  8  =  400  X  2.  From  this  experiment  it 
is  again  evident  that  the  work  done  by  the  force  moving 
the  length  of  the  plane  is  equal  to  the  work  resulting 
from  lifting  the  weight  up  the  vertical  height  of  the 

W       i 

plane,  that  is,  F  X  i  =  W  X  h,  and  — ;  =  — ,  i.  e.  the 

mechanical  advantage  of  the  inclined  plane  is  the  ratio 
of  the  length  of  the  plane  to  the  height  of  the  plane,  or 
the  ratio  of  the  weight  lifted  to  the  force  acting  parallel 
to  the  plane. 

The  use  of  the  inclined  plane  is  for  loading  barrels  or 
logs  on  a  wagon  and  for  unloading  them;  to  roll  or  slide 
objects  down  into  a  cellar  or  for  taking  them  out.  By 
using  a  very  long  plane  heavy  objects  can  be  loaded  on 
a  wagon  with  but  little  force.  If  the  wagon  is  3  feet 
high  and  the  plane  18  feet  long,  a  force  of  100  pounds 
will  roll  a  6oo-pound  barrel  up  on  the  wagon. 

The  grade  of  a  highway  or  railroad  is  the  number  of  feet 
that  the  road  rises  vertically  per  hundred  feet.  A  railroad 
running  straight  up  a  hill  a  mile  long  (5280  feet)  has  a 
grade  of  2  per  cent,  if  the  top  of  the  hill  is  105.6  feet  above 
the  level  of  the  road  at  the  bottom.  The  mechanical  ad- 
vantage of  this  grade  or  inclined  plane  is  5280  feet  -r- 105.6 
feet;  or  50;  hence,  in  order  to  pull  a  train  to  the  summit 


i88 


GENERAL  SCIENCE 


of  the  hill,  the  engine  must  exert  a  continuous  force  equal 
to  XA-  of  the  combined  resistance  of  the  train  of  cars. 


RAILROAD  GRADE  WHERE  ENGINES  ARE  USED  ON  BOTH  ENDS  OF  A  TRAIN 

When  building  railroads  and  highways  the  grades  are 
made  very  gradual  wherever  possible,  because  it  requires 
much  more  work  to  pull  a  loaded  wagon  or  train  of  cars 
up  a  steep  grade  than  up  a  gradual  one  of  the  same  length. 
125.    The  Wedge   is  only  a  modified  inclined  plane. 
Some  kinds  consist  of  a  simple  inclined 
plane  with  a  base  and  slope,  and  others 
consist  of  two  inclined  planes  laid  with 
the  bases  together  and  the  slopes  on 
either  side.     Wedges  are  used  in  split- 
ting logs   and    stone,    raising   heavy 
weights    and    buildings   a  short   dis- 
tance,   launching   ships,   and   similar 
operations. 

Chisels,  axes,  knives,  and  tools  used  for  cutting  are 
examples  of  wedges.     The  common  pin  is  a  wedge  that 


SHOWING  THE  USE  OF 
THE  WEDGE 


SIMPLE  MACHINES  189 

is  widely  used.  Lumbermen  use  both  iron  and  wooden 
wedges  to  split  logs.  An  iron  wedge  8  inches  long  and 
one  inch  thick  at  the  large  end,  has  a  mechanical  ad- 
vantage of  8.  If  this  wedge  is  struck  with  a  five-pound 
hammer  descending  at  a  speed  of  100  feet  per  second,  it 
will  lift  a  weight  of  4,000  pounds.  (The  force  of  the 
hammer  is  100  X  5  or  500  pounds;  500  X  8  =  4,000.) 

126.  The  Screw  is  a  modified  inclined  plane.  The 
threads  of  a  screw  may  be  thought  of  as  an  inclined  plane 
wrapped  around  a  rod.  Since  a 
lever  of  some  kind  is  used  to 
turn  the  screw,  the  whole  ma- 
chine may  be  regarded  as  a  com- 
bination of  the  inclined  plane 
and  the  lever.  When  the  screw 
is  turned  once  around  it  moves  SHOWING  THE  PITCH  OF  A  SCREW 

a  vertical  distance  equal  to  the  distance  between  the 
tops  of  two  adjoining  threads;  this  distance  is  the  space 
between  two  adjoining  threads  plus  the  thickness  of  the 
thread.  This  vertical  distance  is  called  the  pitch  of  the 
screw.  So  when  the  lever  of  a  screw  makes  one  complete 
revolution,  the  object  on  the  screw  is  moved  a  distance 
equal  to  the  pitch  of  the  screw  being  used.  Hence,  the 
mechanical  advantage  of  a  screw  is 
the  result  obtained  by  dividing  the 
distance  moved  by  the  force  used  in 
making  one  complete  revolution, 

SQUARE  THREADS  AND  V     by  the  pitch  of  the  screw.     If  the 

THREADS  OF  A  SCREW  .     ,       ..  .  "  V  •'  ... ,  i     i 

pitch  of  a  screw  is  J  inch  and  the 

lever  2  feet,  the  mechanical  advantage  is  2X2XI2X 
3.1416  -T-  .5,  or  301.5.  If  a  force  of  100  pounds  were  ap- 
plied at  the  end  of  the  lever,  a  weight  of  301.5  X  100,  or 
30,150  pounds,  could  be  lifted,  if  there  were  no  friction. 


igo 


GENERAL  SCIENCE 


Lifting  jacks,  cotton  and  hay  presses,  letter  presses, 
vises,  the  screw  propeller  of  ships,  and  electric  fans  are 


JACK-SCREW 


COPYING  PRESS 


familiar   examples   of   the  practical  uses   to   which   the 
screw  is  put.     It   is  also  commonly  used  in  machinery 

and  woodworking. 
The  micrometer  screw 
can  be  used  to  measure 
the  thickness  of  a  hair. 
The  speed  counter  is  a 
screw  turning  in  a 

A  SCREW  FOR  DETERMINING  THE  SPEED 
OF  ROTATING  WHEELS 


notched    wheel    and    is 
used    to  determine  the 
number  of  revolutions  per  second  made  by  a  wheel. 


Problems.  Find  the  mechanical  advantage  of  an  inclined  plane 
12  feet  long  and  3  feet  high.  Find  the  force  required  to  roll  a 
600  pound  barrel  up  the  plane.  How  much  work  will  be  done  in 
rolling  the  barrel  to  the  top  of  the  plane? 

127.  Pulleys.  —  The  pulley  is  a  modified  first  or  second 
class  lever.  The  center  of  the  pulley  is  the  fulcrum, 
the  force  can  be  thought  of  as  though  it  were  applied  at 
one  end  of  the  diameter  of  the  pulley.  The  weight  is  at 
the  other  end  of  the  diameter,  when  the  pulley  is  a  first- 


SIMPLE   MACHINES 


191 


FIXED  PULLEY 


class  lever.  When  the  pulley  is  a  second-class  lever, 
the  weight  is  at  the  center,  the  force  is  at  one  end  of  the 
diameter,  and  the  fulcrum  is  at  the  other  end. 

(a)  It  is  often  more  convenient  to  have  a  force  act  in  one 
direction  than  in  another,  and  the  pulley  is  a  very  effec- 
tive device  with  which  to  do  this.  It  is 
much  easier  to  have  a  pulley  at  the  top  of 
a  flag  pole,  with  a  rope  around  it,  and  pull 
the  flag  up  by  pulling  downward  on  the 
rope,  than  to  climb  the  mast  and  pull  up 
the  flag.  When  a  pulley  is  fastened  in 
one  position,  as  the  one  at  the  top  of  a 
flag  pole,  it  is  called  a  single  fixed  pulley, 
such  as  is  also  shown  in  the  illustration. 
When  a  single  fixed  pulley  is  used  we  can 
easily  find  by  experiment  that  the  force- 
applied  is  always  equal  to  the  weight  lifted; 
hence  the  mechanical  advantage  is  one,  that  is,  no  ad- 
vantage at  all  except  in  changing  the  direction  of  the  force. 
(6)  The  single  movable  pulley  is  one 
which  is  fastened  to  the  weight  and  moves 
f  as  the  weight  moves,  hence  it  is  called 
movable.  In  the  figure,  one  end  of  the 
rope  is  fastened  on  the  hook  and  the 
other  end  is  attached  to  the  force  /.  The 
pulley  with  the  weight  W  attached  is  rest- 
ing on  the  rope.  Each  strand  of  rope,  c 
or  6,  holds  one-half  the  weight,  just  the 
same  as  if  the  weight  were  hanging  on  two 
separate  ropes.  The  pulley  is  now  acting 

as   a   second-class   lever    whose    fulcrum 
MOVABLE  PULLEY  ,  i  •  i  ,  mi      <•  i 

moves  as  the  weight  moves.     The  fulcrum 

is  at  the  end  of  the  diameter  which  the  strand  of  rope, 


GENERAL  SCIENCE 


coming  from  the  hook,  touches.  The  force  arm  is  the 
whole  diameter  of  the  pulley  and  the  weight  arm  is  one- 
half  the  diameter.  If  the  diameter  is  four  inches,  the 
force  arm  will  be  four  inches  and  the  weight  arm  two 
inches.  The  mechanical  advantage  of  a  single  movable 
pulley,  then,  is  4  -T-  2,  or  2.  Hence  the  force  required  to 
lift  a  2oo-pound  weight  is  100  pounds.  The  other  100 
pounds  of  the  weight  is  held  by  the  strand  of  rope  fas- 
tened to  the  hook.  If  two  persons  held  the  ends  of  a  rope 
with  a  loo-pound  weight  hanging  on  it,  each  one  would 
be  holding  50  pounds,  or  one-half  of  the  100  pounds;  100 
Ib.  -T-  50  Ib.  =  2,  the  mechanical  advantage. 

Since  the  strand  of  rope  fastened  to  the  hook  does  not 
move  when  the  force  lifts  the  weight,  the 
force  will  move  twice  as  fast  as  the  weight. 
When  the  weight  is  lifted  three  feet,  the 
force  will  have  moved  six  feet.  Hence  the 
work  done  by  a  force  of  100  pounds  is  equal 
to  the  work  accomplished  on  a  weight  of  200 
pounds  when  it  is  moved  5  feet:  100  X  10  = 
200  X  5. 

(c)  Combinations  of  Pulleys.  —  When  one 
or  more  fixed  pulleys  are  combined  with  one 
or  more  movable  pulleys,  the  combination 
is  called  a  block  and  tackle.  Heavy  weights 
can  be  lifted  by  such  combinations  with  a 
small  force.  Two  or  more  pulleys  may  be 
fastened  in  one  block,  and  when  this  block 
is  securely  attached,  it  is  called  the  fixed  block  of  pul- 
leys. When  a  block  of  pulleys  is  attached  to  the  weight 
which  is  to  be  moved,  this  is  called  the  movable  block  of 
pulleys,  or  simply  the  movable  pulleys,  because  they  move 
with  the  weight.  The  fixed  pulleys  are  used  only  to  change 


BLOCK  AND 
TACKLE 


SIMPLE   MACHINES  193 

the  direction  of  the  force  with  respect  to  the  weight  and  do 
not  give  any  mechanical  advantage.  Only  the  movable 
pulleys  give  mechanical  advantage.  We  saw  in  division 
(b)  of  this  section  that  the  mechanical  advantage  of  a 
movable  pulley  is  2,  and  that  there  are  two  strands  of  rope, 
one  going  to  the  pulley  and  the  other  coming  from  it. 
So  in  order  to  find  the  mechanical  advantage  of  a  block 
and  tackle,  we  count  the  number  of  movable  pulleys  and 
multiply  that  number  by  2,  or  count  the  number  of  strands 
of  rope  going  to  and  from  the  movable  pulleys;  the 
results  are  the  same,  if  the  rope  is  first  attached  to  the 
fixed  pulleys.  In  a  system  of  two  movable  pulleys  with 
a  mechanical  advantage  of  4,  a  force  of  100  pounds  can 
lift  a  4oo-pound  weight.  Since  there  are  four  strands  of 
rope,  the  force  will  move  four  times  as  fast  as  the 
weight  and  also  move  four  times  as  far  as  the  weight; 
hence  the  work  done  by  the  force  will  again  be  equal  to 
the  work  accomplished  on  the  weight. 

Combinations  of  pulleys  are  used  in  moving  heavy  fur- 
niture, pulling  stumps,  lifting  heavy  stones  and  timbers, 
moving  small  buildings,  and  in  various  other  applications. 

Problems.  1.  What  force  will  be  required  to  lift  a  2Oo-pound 
weight  with  a  single  fixed  pulley?  With  a  single  movable  pulley? 

2.  Find  the  force  needed  to  lift  a  6oo-pound  piano  to  a  second 
story  window  with  a  block  and  tackle  containing  two  movable 
pulleys.     If  the  window  is  10  feet  high,  how  far  will  the  force  move 
while  pulling  the  piano  up? 

3.  What  is  the  least  number  of  movable  pulleys  that  can  be 
used  in  a  block  and  tackle  to  lift  a  24oo-pound  weight  with  a  force 
of  300  pounds.     How  far  will  the  weight  move  if  the  force  moves 
72  feet? 

4.  What  is  the  largest  weight  that  can  be  lifted  by  a  force  of 
250  pounds  applied  to  a  block  and  tackle  containing  six  movable 
pulleys?     How  far  will  the  force  have  to  move  to  lift  the  weight 
5  feet? 


194 


GENERAL   SCIENCE 


ONE  FORM  or  WHEEL  AND  AXLE 


128.  Wheel  and  Axle. --The  wheel  and  axle  consists 
of  a  large  wheel  fastened  to  an  axle  which  extends  out 
from  the  wheel  far  enough  so  that  a  rope  can  be  wound 
on  it.     Its   mechanical   advantage  is   explained   by   the 

principle  of  the  lever.  The 
radius  of  the  axle  is  the 
weight  arm,  the  radius  of 
the  wheel  is  the  force  arm, 
and  the  center  of  the  axle 
is  the  fulcrum  about  which 
the  two  arms  turn.  So  the 
mechanical  advantage  of 
the  wheel  and  axle  is  equal 
to  the  radius  of  the  wheel 

divided  by  the  radius  of  the  axle.     Sometimes  the  rope  is 

wound  on  both  axle  and  wheel  but  in  opposite  directions. 

If  the  radius  of  the  wheel  is  2  feet  and  the  radius  of  the 

axle  is  6  inches,  the  mechanical  advantage  is  24  in.  -f-  6  in. 

or  4.     With  such  a  system 

a  force  of  100  pounds  will 

balance  a  weight  of  400 

pounds    attached    to   the 

rope  wound  on  the  axle. 
The  Capstan  is  a  form 

of  the  wheel  and  axle:  the 

lever   corresponds   to   the 

radius  of  the  wheel,  and 

the  radius  of  the  barrel  corresponds  to  the  radius  of  the 

axle. 

129.  Windlass  and  Cogwheels.  --  The  windlass,  which 
is  extensively  used  for  drawing  water  from  wells,  is  a 
form  of  wheel  and  axle.     When  it  is  turned,  the  crank 
handle  describes  a  circle  which  corresponds  to  the  wheel 


CAPSTAN  or  A  VESSEL 


SIMPLE   MACHINES 


195 


of  the  wheel  and  axle.     The  mechanical  advantage  of 
the  windlass  is  equal  to  the  result  obtained  by  dividing 
the  radius    of  the  circle  described 
by  the  crank  by  the  radius  of  the 
axle. 

Cogwheels  are  also  modifications 
of  the  wheel  and  axle,  but  the  wheels 
which  turn  each  other  are  fastened 
on  different  axles.     The  number  of 
cogs  on  the  large  wheel  divided  by 
the  number  of  cogs  on  the  small 
wheel,  will  give  the  mechanical  ad- 
vantage;  or  the  radius  of  the  large 
wheel  divided  by  the  radius  of  the    COMPOUND  WINDLASS  OF  A 
small  wheel  will  also  give  the  me- 
chanical advantage.     The  sizes  of  the  wheels  can  be  made 
to  have  such  a  relation  to  each  other  that  a  very  heavy 
weight  can  be  lifted  by  a  small  force. 

Cogwheels  are  also  used  to  control  the  speed  of  ma- 
chinery. Where  high- 
speed engines  are  used, 
as  in  the  automobile,  the 
cogwheel  attached  to 
the  engine  shaft  is  a 
small  one  which  turns  in 
a  larger  one,  thus  reduc- 
ing the  speed  of  the 
wheels  of  the  automo- 
bile. High  speed  of  ma- 
chinery can  be  obtained 


GEARING  OF  AN  AUTOMOBILE 


by  applying  the  force  to  a  large  cogwheel  which  turns  a 
small  one,  or  even  a  series  of  smaller  ones,  as  is  done  on 
the  cream  separator. 


GENERAL  SCIENCE 


Belts  and  belt  wheels  are  used  for  changing  the  speed 
of  machinery  and  for  the  transmission  of  energy  over  a 
considerable  distance  so  that  it  can  be  utilized  in  another 
place. 

Very  complex  or  compound  machines  can  be  made  by 
combining  two  or  more  of  the  simple  machines.  The 
mechanical  advantage  of  a  compound  machine  is  equal 
to  the  product  obtained  by  multiplying  together  all  the 
mechanical  advantages  of  the  sim- 
ple machines  included  in  the  struc- 
ture of  the  compound  one.  By 
such  combinations  a  very  high 
mechanical  advantage  can  be  ob- 
tained. Derricks  or  travelling 
cranes  used  by  railroads  are  usually 
combinations  of  block  and  tackle, 
cogwheels,  and  a  windlass  on  which 
to  wind  the  rope.  The  machinery 
in  factories,  printing  establish- 
ments, and  on  Western  farms  is 
very  complex,  and  these  machines 
require  a  considerable  amount  of 
knowledge  on  the  part  of  the  per- 
Every  successful  farmer  of  today 
must  be  more  or  less  of  a  machinist. 

130.  Power.  —  Review  energy,  force,  and  work  in  §  117 
of  this  chapter.  Power  is  the  rate  at  which  work  is  done, 
or  it  is  the  time  rate  of  doing  work.  The  word  work 
does  not  include  time.  It  requires  just  as  much  work 
to  carry  200  bricks  to  the  top  of  a  20-foot  building  in  two 
days  as  it  does  to  carry  them  up  in  two  hours.  We  do 
just  as  much  work  when  we  walk  to  the  top  of  a  hill  as 
when  we  run  up.  The  force  which  we  exert  is*  much 


HAND  DERRICK 
With  hoisting  tackle  of 
rope  and  pulleys. 

sons  operating  them. 


SIMPLE   MACHINES  197 

less  when  we  walk  up  than  when  we  run  up  the  hill. 
The  energy  consumed  in  both  cases  is  the  same,  but  to 
run  up  consumes  energy  faster  than  to  walk  up.  An 
engine  that  can  do  100  foot  pounds  of  work  in  a  second 
has  more  power  than  one  which  can  only  do  50  foot 
pounds  in  a  second;  that  is,  the  former  engine  can  liberate 
energy  faster  than  the  latter.  The  former  engine  can 
also  do  more  work  in  a  day  than  the  latter  one.  Since 
work  and  time  can  be  measured,  the  power  of  a  machine 
can  also  be  measured  by  .finding  how  much  work  it  can 
do  in  a  unit  of  time.  Since  the  unit  of  work  in  the  English 
system  is  the  foot  pound  and  the  unit  of  time  is  the  second, 
the  unit  of  power  is  a  foot  pound  of  work  per  second,  or 

F  Xd       W 

P  = =  —  =  one  foot  pound  per  second  when 

t  t 

W  and  /  are  unity.  The  work  accomplished  by  a  machine, 
divided  by  the  time  required  to  do  the  work,  gives  the 
power  of  the  machine. 

As  the  inch  is  too  small  a  unit  for  measuring  long 
distances,  so  the  foot  pound  per  second  is  too  small  a 
unit  with  which  to  measure  the  power  of  engines.  James 
Watt,  the  inventor  of  the  steam  engine,  chose  a  larger 
unit,  namely,  550  foot  pounds  per  second,  for  measuring 
the  power  of  engines;  550  foot  pounds  per  second  is  called 
the  horse  power  (H.P.),  because  it  was  thought  that  an 
average  horse  could  do  550  foot  pounds  of  work  in  a 
second.  The  power  of  an  average  man  is  about  one- 
seventh  of  a  horse  power.  Railroad  locomotives  have 
several  hundred  horse  power,  varying  from  500  to  1000, 
and  the  combined  power  of  the  engines  of  an  ocean  liner 
is  many  thousand  H.P.,  sometimes  as  much  as  70,000  H.P.1 

1  In  the  metric  system  the  erg  is  the  absolute  unit  of  work,  so  the 
corresponding  unit  of  power  is  the  erg  per  second.  This  unit  of  power  is 


ig8  GENERAL   SCIENCE 

Since  man  himself  does  not  have  sufficient  physical 
power  to  operate  large,  complex  machines,  he  has  learned 
to  use  the  power  (i)  of  animals,  (2)  of  engines  in  which 
the  power  for  their  operation  comes  from  the  fuel  burned 
in  them,  (3)  of  rivers  and  waterfalls  which  are  made  to 
flow  over  water  wheels  and  develop  power  to  run  other 
machinery,  (4)  of  the  wind  by  building  windmills  for 
pumping  water,  and  even  (5)  the  power  of  the  rays  of 
the  sun  by  building  sun  engines  which  transform  the 
energy  of  the  sun's  rays  into  mechanical  energy;  these 
engines  can  only  be  run  while  the  sun  is  shining,  so  a 
warm  country  with  a  cloudless  sky  is  necessary  for  their 
successful  operation. 

QUESTIONS    AND    EXERCISES 

1.  What  are  some  of  the  forces  of  nature  that  man  has  con- 
quered ?     What  use  does  he  make  of  them  ? 

2.  When  and  by  whom  were  the  following  invented:  the  tele- 
phone, telegraph,  sewing  machine,  biplane,  and  steamboat  ? 

3.  Define  energy,  force,  distance,  work,  and  power. 

4.  Define  the  units  of  work  and  the  units  of  power. 

5.  Draw  the  three  classes  of  levers  and  name  their  parts. 

6.  Why  is  it  better  that  the  long  bones  of  our  bodies  are  used 
as  levers  of  the  third  class  ? 

7.  Why  do  modern  road-builders  cut  through  hills  and  fill  low 
places  ?     What  is  a  3  per  cent  grade  ? 

8.  Does  a  combination  of  pulleys  save  work  or  waste  work  ? 

9.  How  find  the  advantage  that  the  force  applied  has  over  the 
weight  being  lifted  by  a  compound  machine  ? 

so  small  that  it  is  customary  to  take  as  the  practical  unit  10,000,000  ergs 
per  second.  This  large  unit  is  called  the  watt,  in  honor  of  James  Watt. 
Since  the  power  of  dynamos  and  electric  motors  is  so  great,  a  still  larger 
unit  is  used  to  measure  their  power,  called  the  kilowatt,  which  is  equal  to 
1,000  watts.  Engines  are  also  being  measured  in  kilowatts  rather  than  in 
H.P.  A  horse  power  is  equivalent  to  746  watts,  or  about  three-fourths  of 
a  kilowatt. 


CHAPTER  XX 
WATER   WHEELS   AND    WINDMILLS 

131.  Water  Power.  —  Every  boy  who  has  played  in 
a  running  stream  or  with  a  sprinkling  hose  knows  that 
swiftly  flowing  water  has  considerable  force.  It  requires 
much  greater  effort  to  row  a  boat  upstream  than  to  row 
it  downstream  at  the  same  rate.  Water  exerts  a  force 
in  the  direction  in  which  it  flows  and  so  resists  objects 
moving  against  the  current  and  assists  the  movement  of 
objects  which  are  going  in  the  same  direction  as  the 
current.  If  a  steamboat  can  go  upstream  six  miles  per 
hour  when  the  current  is  moving  three  miles  per  hour,  the 
same  boat  can  go  downstream  at  the  rate  of  twelve  miles 
per  hour.  In  this  case  it  requires  twice  as  much  work 
for  the  boat  to  go  upstream  as  to  go  down  the  same 
distance.  To  overcome  the  resistance  of  flowing  water 
is  no  small  task  in  ocean  and  river  commerce.  The 
captains  of  ocean  liners  aim  to  run  their  vessels  with  the 
ocean  currents  as  much  as  possible. 

Mountain  streams  and  waterfalls  can  be  made  to  develop 
sufficient  power  to  run  mills,  factories,  and  street  cars, 
to  light  the  streets  and  homes,  and  even  to 'heat  build- 
ings. Niagara  Falls,  the  greatest  cataract  in  the  world, 
is  used  by  both  the  United  States  and  Canada  for  the 
development  of  power,  mostly  in  the  form  of  electricity. 
Every  pound  of  water  in  the  Niagara  River  does  about 
150  foot  pounds  of  work  when  it  plunges  over  the  falls. 
The  millions  of  pounds  of  water  of  the  Niagara,  if  utilized, 


200 


GENERAL  SCIENCE 


would  develop  enough  power  to  supply  the  needs  of 
many  cities.  But  the  natural  scenery  of  such  a  cataract 
is  considered  to  be  worth  more  to  civilization  than  the 
work  which  could  be  done  by  using  its  power. 

To  make  waterfalls  for  the  development  of  power,  a 
dam  is  usually  built  in  rivers  and  mountain  streams. 
These  dams  also  help  to  regulate  the  supply  of  water 
and  to  keep  it  under  control.  The  supply  of  water 
must  be  constant  in  order  to  operate  machinery  success- 
fully. Nearly  all  of  the  flour  mills  built  by  the  early 
settlers  of  the  United  States  were  run  by  water  power. 
Many  of  these  can  now  be  found  in  ruins.  The  largest 
flour  mills  in  the  world  are  run  by  water  from  the  Missis- 
sippi river  at  St.  Paul,  Minnesota.  Nearly  all  of  the 
water  of  the  Androscoggin  River  is  used  for  power  in 
Lewiston,  Maine.  This  is  true  of  many  other  rivers. 
There  are  several  types  of  water  wheels  now  in  use. 

They  are  all  made  to  receive 
the  energy  of  the  flowing 
water  and  transform  it  into 
mechanical  energy.  The  type 
of  wheel  used  is  determined  by 
the  quantity  of  water  avail- 
able and  the  distance  that  it 
falls.  The  various  types  are 
the  following. 

132.  The  Overshot  Wheel. 
-The  overshot  wheel  as 
shown  in  the  illustration  is 
made  of  a  series  of  trough- 
like  buckets  into  which  the 
water  pours  at  the  top.  The  buckets  empty  their  water 
at  the  bottom  of  the  wheel  and  go  up  empty  and  upside 


OVERSHOT  WATER  WHEEL 


WATER  WHEELS  AND  WINDMILLS  201 

down.  The  weight  and  force  of  the  water  flowing  into  the 
buckets  turn  the  wheel.  This  overshot  wheel  is  used  where 
the  fall  is  not  very  great  and  its  diameter  is  almost  equal 
to  the  distance  the  water  falls.  The  waste  in  power  is 
due  largely  to  the  water  spilling  out  of  the  buckets  or 
shooting  over  them.  The  efficiency  of  such  a  wheel  is 
from  80  per  cent  to  90  per  cent.  The  power  is  transmitted 
by  a  shaft  and  series  of  cogwheels  or  by  a  belt. 

133.  The  Undershot  Water  Wheel.  —  This  is  used  in 
level  countries  where  the  fall  of  water  is  not  great  enough 
for  overshot  wheels, 

but  where  the  water 
is  in  abundance.  The 
wheel  is  built  some- 
what like  the  pad- 
dle-wheel  on  a 
steamboat,  and  the 
water  strikes  the 
wheel  at  the  bottom 
with  the  force  with 
which  it  flows  into  UNDERSHOT  WHEEL 

the  mill-race  from  the 

bottom  of  the  dam.  A  type  of  the  undershot  water  wheel 
is  the  one  which  boys  usually  make  while  playing  in  swiftly 
running  streams.  The  efficiency  of  the  undershot  wheel 
is  about  30  per  cent  when  compared  to  the  energy  of  the 
water  above  the  dam. 

134.  The  Pelton  Water  Wheel  or  Motor.  —  This  is  a 
modern  form  of  the  undershot  wheel  which  has  come  into 
use  since   1880.     Small  forms  of  it  are  used  for  small 
power  machines  in  cities  in  which  power  can  be  had  from 
the  waterworks.     It  is   also   used  where  water  is   con- 
ducted  down   a   mountain    through   pipes.     The   water 


202 


GENERAL  SCIENCE 


flows   from   a   nozzle   against   spoon-like   blades   on   the 

wheel.     The  efficiency  of  such  wheels  may  be  as  high 

as  84  per  cent. 

135.   The  Turbine  Water  Wheel  is  made  of  thin  blades 

set  at  such  an  angle 
that  the  water  can 
strike  them  and  cause 
the  wheel  to  rotate.  It 
is  enclosed  in  an  iron 
casing  into  which  the 
water  is  permitted  to 
flow  for  turning  the 
wheel.  The  water  falls 
through  the  penstock 

and  exerts  a  force  that  causes  the  wheel  to  rotate  rapidly. 
The  turbine  wheel  was  invented  in  1883  and  is  now 

used   more   than   any   other   wheel.     It   gives   the   best 


P  ELTON  WHEEL 


Outer  case  Inner  case 

PARTS  OF  A  TURBINE 


Turbine  wheel 


results  if  a  waterfall  of  10  feet  or  more  can  be  secured. 
It  is  used  exclusively  at  Niagara,  where  the  water  drops 
more  than  100  feet  before  going  through  the  turbine 
wheel.  Some  of  the  turbines  at  Niagara  develop  5,000 
horse  power.  One  of  the  most  powerful  turbines  in 
use  is  at  Quebec,  Canada.  The  water  falls  135  feet,  the 


WATER  WHEELS   AND   WINDMILLS 


203 


wheel  is  10  feet  in  diameter,  and  develops  10,500  horse 
power. 

The  energy  of  the  turbine  wheel  is  transmitted  by  a 
shaft  to   an   electric  dynamo   or  other 
machinery.     There   are   turbine  wheels 
which  transmit  for  use  90  per  cent  of 
the  energy  of  the  falling  water. 

The  diagrams  illustrate  the  parts  of  a 
turbine  and  one  installed. 

136.  Value  of  a  Stream  or  Waterfall. 
-  Before  any  kind  of  water  wheel  is 
installed  the  quantity  of  water  and  the 
distance  it  can  be  made  to  fall  are 
ascertained  in  order  to  determine  the 
kind  and  size  of  wheel  to  use.  A  small 
wheel  cannot  transform  all  the  energy  of 

a  large  supply  of  water,    and   a    large 

.      ,  11  u  -*u  TURBINE  AT  NIAGARA 

wheel  cannot  develop  much  power  with  FALLS 

a  small  quantity  of  water. 

The  quantity  of  water  delivered  by  a  stream  can  be 
determined  as  follows:  Measure  the  width  of  the  stream 
and  the  depth  at  intervals  of  5  or  10  feet  and  take  the 
average  depth.  Measure  the  speed  of  flow  of  the  water 
by  placing  a  float  in  the  middle  of  the  stream  and 
see  how  far  it  moves  in  a  minute.  For  example,  sup- 
pose the  stream  is  50  feet  wide;  if  the  depths  are  4,  6, 
9,  7,  and  5  feet,  the  average  depth  would  be  (4  +  6  +  9 
+  7  +  5)  -=-  5  =  65  feet-  Suppose  the  stream  flows  4 
feet  per  second.  The  quantity  of  water  that  would  flow 
over  a  dam  in  a  second  would  be  50  X  6^  X  4  feet>  or 
1240  cubic  feet.  A  cubic  foot  of  water  weighs  62.5 
pounds.  So  the  weight  of  water  flowing  over  the  dam 
per  second  would  be  1240  X  62.5  pounds,  or  77,500 


204  GENERAL  SCIENCE 

pounds.  If  the  dam  is  12  feet  high,  the  work  which  the 
water  would  do  per  second  would  be  77,500  pounds  X 
12  feet,  or  930,000  foot  pounds.  It  would  develop 
930,000  4-  550  or  1690.9  horse  power  if  there  were  no 


DAM  IN  THE  ALLEGHENY  RIVER 

waste.  Such  a  stream  would  be  valuable  for  running  a 
flour  mill  or  other  machinery,  but  the  turbine  installed 
should  be  one  which  would  develop  about  1,000  horse 
power,  as  all  of  the  water  could  not  be  made  to  pass 
through  the  wheel. 

137.   Windmills.  —  The    toy    wind    wheel    made    of 
paper  and  fastened  to  a  stick  with  a  pin, 
illustrates    the    principle  of  the   windmill. 
The  air  strikes  the  curved   blades  of   the 
wheel  at  an  angle  and  the   wheel   is   thus 
turned  by  the  force  of  the  air.     The  wheel 
TOY  WIND      of  a  windmill  is   made  of  strong  blades  of 
wood  or  steel,   sometimes  curved  like   the 
blades  of  a  toy  wheel;   sometimes  the  blades  are  flat  but 
set  at  an  angle  so  that  the  force  of  the  wind  causes  the 


WATER  WHEELS  AND  WINDMILLS 


205 


wheel  to  rotate.  The  principle  of  the  windmill  is  the 
same  as  that  of  the  turbine  water  wheel ;  the  moving  sub- 
stance or  fluid  strikes  the  blades  of  the  wheel  at  an  angle 
in  each  case  and  thus  imparts  mechani- 
cal energy  to  the  wheel.  The  axle  of 
the  wheel  of  the  windmill  is  rigidly 
fastened  to  the  wheel.  The  axle  has 
fastened  to  it  a  cogwheel  that  turns 
another  wheel  with  a  crank  attached 
which  moves  the  piston  of  the  pump  up 
and  down  as  the  wheel  turns  around. 

The  wheel  of  a  windmill  will  not  turn 
when  it  stands  edgewise  to  the  wind. 
It  must  stand  perpendicular  to  the 
wind,  that  is,  face  the  wind,  in  order  to 
rotate.  A  tail -like  fan  is  used  to  cause 
the  wheel  to  face  the  wind.  When  the 
fan  is  perpendicuar  to  the  wheel  the 
wheel  will  face  the  wind  and  rotate,  but 
when  the  fan  is  pulled  so  that  it  stands 
edgewise  with  the  wheel,  the  wheel  will 
not  rotate.  By  shifting  the  fan  the 
wheel  is  thrown  in  or  out  of  action.  Most  windmills 
are  constructed  so  that  they  throw  themselves  out  of 
action  when  the  wind  blows  extremely  hard. 

Windmills  are  used  mostly  for  pumping  water.  The 
water  is  kept  out  of  the  lowlands  of  Holland  by  wind- 
mills which  are  very  numerous  and  work  while  the  wind 
blows.  Many  farmers  use  windmills  for  pumping  water 
for  their  live-stock  and  for  their  homes.  The  water  is 
generally  pumped  into  an  elevated  tank.  From  these 
tanks  it  is  piped  into  the  house  for  use  in  the  various 
rooms  and  sometimes  piped  into  the  barn  for  the  stock. 


WINDMILL 


206  GENERAL  SCIENCE 

In   this   way  farmers   enjoy   the   use   and   advantage   of 
waterworks  the  same  as  the  people  in  the  city. 

QUESTIONS    AND    EXERCISES 

1.  Where  have  you  seen  a  natural  waterfall  or  a  dam  ?      What 
practical  use  can  be  made  of  such  places  ? 

2.  What  use  could  a  man  make  of  a  swiftly-flowing  stream  pass- 
ing through  his  farm? 

3.  Make  a  water  wheel  and  try  it  in  some  flowing  water. 

4.  Make  a  small  windmill  and  fasten  it  in  some  exposed  position 
and  observe  how  the  wind  affects  it.     What  practical  use  is  made 
of  such  machines? 


CHAPTER  XXI 
STEAM    AND    GAS   ENGINES 

138.  Steam  is  water  vapor  or  water  in  gas  form  which 
has  a  temperature  of  100°  C.  at  standard  pressure.     When 
water   changes   to   steam  it  increases  in  volume   about 
i ,600  times,  that  is,  one  gallon  of  water  will  make  1,600 
gallons  of  steam  and  fill  a  space  of  214  cubic  feet  at 
standard   pressure.     The   molecules   of   steam   are   very 
active  and  move  about  with  high  speed.     The  speed  of 
the  molecules  varies  with  the  temperature.     To  change 
water  at  boiling  point  to  steam  requires  536  calories  for 
each  gram  of  water,  and  the  steam  has  the  same  tempera- 
ture as  the  boiling  water.     These  536  calories  of  heat  are 
used    to   make  the  molecules  move  faster.     The  faster 
they  move  the  more  space  a  given  number  of  them  re- 
quires and  the  harder  they  strike  against  the  walls  of 
the  vessel  enclosing  them.     Since  the  molecules  of  steam 
move  at  such  a  high   speed   they  will   rush  with  great 
force  through  any  valve  or  opening  that  is  made  in  the 
containing  vessel.     The  energy  of  the  steam  is  derived 
from  the  wood  or  coal  which  is  oxidized  to  make  heat. 

139.  The  Steam  Engine.  —  More  than  150  years  ago 
James  Watt,   an  instrument  maker  living  in  England, 
studied  the  crude  engines  in  use  in  his  day  and  invented 
the  double-action  steam  engine,  which  was  the  same  in 
principle  as  the  steam  engines  of  the  present  time.     Most 
of  the  improvements  that  have  been  made  on  Watt's  in- 
vention have  been  on  the  machinery  to  which  the  engine 


208 


GENERAL   SCIENCE 


is  attached,  and  of  course  many  changes  have  been  made 
in  the  mechanism  of  the  engine  itself,  but  there  has  been 
no  change  in  principle. 

The  operation  of  a  double-acting  steam  engine  can  be 
understood  from  the  diagram  shown  in  the  illustration. 
The  steam  generated  by  the  fire,  F,  in  the  boiler,  B,  passes 
through  the  pipe,  P,  into  the  steam  chest,  C,  and  thence 
through  the  passage,  0,  into  the  cylinder,  N,  where  its 


THE  PARTS  or  A  STEAM  ENGINE 

pressure  forces  the  piston,  5,  to  the  left.  It  can  be  seen 
from  the  diagram  that,  as  the  driving  rod,  R,  moves 
toward  the  left,  the  eccentric  rod,  H,  which  controls  the 
valve,  V,  moves  toward  the  right.  When  the  piston  has 
reached  the  left  end  of  its  stroke,  the  passage  O  will  have 
been  closed,  while  the  passage  D  will  have  been  opened, 
thus  permitting  the  steam  to  flow  into  the  left  end  of  the 
cylinder,  which  will  force  the  piston  to  the  right  and 
force  the  spent  steam  on  the  right  of  the  piston  out 
through  the  exhaust  pipe,  E.  The  eccentric  rod,  H, 
moves  the  double  valve  in  the  steam  chest,  which  opens 
and  closes  the  passages  0  and  D  alternately  at  just  the 


STEAM   AND    GAS   ENGINES 


209 


proper  moments  to  keep  the  piston  moving  back  and 
forth  throughout  the  length  of  the  cylinder.  The  shaft, 
Sh,  carries  a  heavy  fly  wheel,  W,  which,  after  being 
started,  keeps  the  engine  running  at  constant  speed. 
The  rotary  motion  of  the  shaft  can  be  communicated  to 
any  desired  machin- 
ery by  means  of 
cogwheels  or  of  a 
belt  which  passes 
over  a  pulley  securely 
fastened  to  the  shaft. 

140.  Uses   of  the 
Steam  Engine.  ~ 
Steam    engines    are 
classed  according  to 
use.     Stationary  en- 
gines  do  not    move 
about  and  are  used 
to    operate    factory 
machinery,  run  elec- 
tric dynamos,   etc.      FIXED  BLADES  OF  STEAM  TURBINE  ENGINE 

Traction  engines  are      They  direct  the  steam  against  the  blades  of 

the  rotating  shaft. 

used    for    drawing 

heavy  loads  through  the  country,  for  drawing  gang 
plows  and  harvesters  on  the  Western  plains,  for  run- 
ning threshing  machines,  etc.  Street  steam  rollers  are 
forms  of  traction  engines.  The  railroad  locomotive 
is  a  form  of  traction  engine  fitted  to  run  only  on  steel 
rails.  The  power  of  ordinary  traction  engines  varies 
from  10  to  20  horse  power,  while  railroad  locomotives 
vary  from  500  to  1000  horse  power. 

141.  Steam  Turbines. -- The  steam  turbine  is  a  form 
of  steam  engine  without  back-and-forth  motion  such  as 


210  GENERAL   SCIENCE 

there  is  in  the  piston  of  the  double-action  engine.  The 
principle  of  the  steam  turbine  is  the  same  as  that  of  the 
water  turbine  or  the  wheel  of  a  windmill.  A  wheel 
with  a  great  number  of  blades  like  the  wheel  of  a  wind- 
mill is  firmly  fastened  to  a  shaft;  steam  from  nozzles  is 
directed  against  the  blades  of  the  turbine  wheel  and  the 
wheel  is  thus  caused  to  rotate  at  a  very  high  speed. 


BLADES  ON  THE  ROTATING  SHAFT  OF  STEAM  TURBINE 

The  steam  enters  at  the  middle,  divides,  and  goes  toward 
each  end,  causing  the  shaft  to  rotate  at  high  speed. 

The  steam  can  be  used  several  times  by  allowing  it  to 
pass  over  the  blades  of  several  wheels  which  are  set  in 
series.  Steam  turbines  are  used  where  high  speed  and 
great  power  are  needed,  as  on  modern  ocean  vessels,  the 
engines  of  some  of  which  have  70,000  horse  power.  One 
of  the  Pittsburgh  city  water  pumping  stations  has  a 
steam  turbine  which  runs  a  centrifugal  pump  that  will 
throw  100,000,000  gallons  of  water  in  24  hours. 

142.  Gas  Engines.  —  In  recent  years  gas  engines  have 
come  into  use  for  small  power  purposes  and  to  a  very 
great  extent  have  taken  the  place  of  steam  engines.  Gas 
engines  are  driven  by  properly  timed  explosions  by  an 
electric  spark,  of  a  mixture  of  gas  and  air  within  the 
cylinder.  A  gas  engine  with  a  single  cylinder  has  a 
heavy  pair  of  fly  wheels,  because  the  piston  receives  energy 


STEAM   AND    GAS   ENGINES 


211 


from  exploding  gas  only  at  every  other  rotation  of  the 
fly  wheels.  The  energy 
stored  in  the  fly  wheels 
by  one  explosion  keeps 
the  machinery  running 
until  another  explosion. 
High  power  gas  engines 
have  two  or  more  cylin- 
ders in  which  explosions 

occur  alternately,   thus  GAS  ENGINE 

the  loss   of  power  and 

speed  between  explosions  is  avoided.  The  best  auto- 
mobile engines  have  from  six  to  twelve  cylinders  which 
insure  a  continuous  supply  of  power  and  not  by  jerks 
as  given  by  a  single  cylinder  engine.  The  development 
and  perfection  of  the  gas  engine  have  made  the  auto- 
mobile a  very  effective  machine  and  have  also  made  it 
possible  for  aeroplanes  to  fly  with  considerable  safety. 

The    diagrams    illus- 

E-   ' 


trate  the  operation  of 
one  cylinder  of  a  gas 
engine.  In  No.  i  a 
mixture  of  gas  and  air 
is  being  drawn  into  the 
cylinder  through  the 
valve  as  the  piston,  P, 
moves  to  the  right.  In 
No.  2  the  valves  are 
closed,  and  the  piston  moving  to  the  left  compresses  the 
mixed  gases.  In  No.  3  just  as  the  piston  starts  to  move 
to  the  right  an  electric  spark  which  ignites  the  gas  is 
made  in  the  cylinder,  and  an  explosion  results  which 
drives  the  piston  to  the  right  with  considerable  force 


3.   Explosi 


4. 


PRINCIPLE  OF  THE  GAS  ENGINE 


212  GENERAL  SCIENCE 

and  imparts  its  energy  to  the  heavy  fly  wheel,  which  is 
set  in  rapid  motion.  In  No.  4  as  the  motion  of  the 
fly  wheel  now  drives  the  piston  to  the  left,  the  exhaust 
valve,  D,  is  automatically  opened,  and  the  spent  gas 
escapes,  making  the  characteristic  noise  of  the  gas  engine. 
The  next  movement  of  the  piston  is  the  same  as  in  No. 
i,  and  the  same  cycle  of  motions  is  repeated. 

143.  Efficiency  of  Engines.  —  The  mechanical  effi- 
ciency of  the  gas  engine  is  the  highest  of  all  heat  engines, 
becoming  as  much  as  25  per  cent,  which  is  nearly  twice 
that  of  ordinary  steam  engines.  The  gas  engine  is  free 
from  smoke  (the  smoke  made  by  some  automobiles  is 
due  to  the  oxidation  of  an  excess  of  lubricating  oil  in  the 
cylinders)  and  can  be  started  without  delay,  but  the  fuel 
is  comparatively  expensive. 

The  efficiency  of  the  best  steam  engines  is  about  17 
per  cent,  while  the  efficiency  of  locomotives  is  about 
8  per  cent,  that  is,  only  8  per  cent  of  the  heat  energy  of 
the  coal  which  is  burned  is  transformed  into  mechanical 
energy  by  the  locomotive  while  it  is  running.  The  effi- 
ciency of  steam  turbines  is  as  high  as  that  of  the  best 
double-acting  engines.  The  advantages  of  the  turbines 
are  that  they  run  smoothly,  can-  develop  high  speed, 
and  occupy  only  about  one-tenth  as  much  floor  space  as 
ordinary  engines  of  the  same  power. 

QUESTIONS    AND    EXERCISES 

1.  Can  steam  be  seen  ?     Is  it  heavier  or  lighter  than  ait  ? 

2.  Who  invented  the  steam  engine  ?     When  ? 

3.  Name  the  kinds  of  steam  engines  that  you  have  seen. 

4.  What  is  the  difference  between  a  gas  engine  and  a  steam 
engine  ? 

5.  Where  is  the  fire  in  a  gas  engine  ? 

6.  How  does  the  gas  engine  get  its  power  to  run  ? 


CHAPTER  XXII 
WATER   OR   LIQUID    PUMPS 

144.  Influence  of  Air  in  Pumping  Liquids.  —  Air  has 

weight  and  each  square  inch  of  surface  at  sea  level  is 
holding  up  about  15  pounds  of  air,  that  is,  the  air  exerts 
a  pressure  of  15  pounds  per  square  inch;  15  pounds  of 
pressure  will  sustain  a  column  of  mercury  30  inches 
high.  Since  mercury  is  13.6  times  as  heavy  as  water, 
the  air  will  sustain  a  column  of  water  34  feet  high  if  there 
is  no  air  pressure  on  top  of  the  water.  When  the  air  is 
removed  from  a  tube  which  is  standing  in  water,  the  air 
pressure  on  the  water  outside  the  tube  will  force  the 
water  up  the  tube.  When  we  drink  a  liquid  through  a 
straw,  we  remove  the  air  pressure  from  the  end  which  is 
in  the  mouth,  and  then  the  air  pressing  on  the  liquid  in 
the  vessel  forces  the  liquid  up  the  straw. 
But  we  could  not  drink  water  through  a 
tube  35  feet  high.  Why? 

145.  The   Siphon.  —  The    siphon    may 
be  a  U-shaped  tube  with  the  arm  outside 
the  liquid  longer  than  the  arm  extending 
down  into  the  liquid.     The  liquid  in  the 

tube  is  trying  to  flow  in  both  directions 

J     6  THE  SIPHON 

from  the  point  C.     The  liquid  in  CD  is 
exerting  a  pressure  on  the  liquid  in  the  vessel,  while  the 
liquid  in  CB  is  exerting  a  downward  pressure  greater 
than   that   of  CD,  since  it  is  longer  than  CD  by  AB. 
When   two   unequal   forces    resist    each    other   there   is 


214 


GENERAL   SCIENCE 


motion  in  the  direction  of  the  greater  force.  The  air 
pressure  at  B  is  the  same  as  the  air  pressure  on  the 
liquid  in  the  vessel,  so  it  is  the  difference  between  the 
downward  pressure  of  the  two  columns  of  water  in  CD 
and  CB  that  causes  the  water  to  flow.  The  liquid  flow- 
ing from  C  to  B  tends  to  produce  a  vacuum  at  C,  while 
the  air  pressure  on  the  liquid  in  the  vessel  forces  it  up 
the  tube  CD;  this  process  keeps  the  liquid  flowing. 

146.   The  Common  Lifting  Pump.  —  If  one  end  of  a 
tube  containing  a  piston  is  placed  in  water  and  the  piston 
drawn  up  quickly,  the  water  will  follow 
the  piston  up  the  tube.     This  occurs 
because   the  motion  of  the  piston  re- 
duces the  pressure  on  the  water  in  the 
tube,  and  then  the  pressure  of  the  air 
on  the  water  outside  the  tube  forces 
the  water  up   the   tube,  the  same  as 
when   we    take   lemonade    through    a 
straw  by  reducing  the  air  pressure  at 
the   end   of   the  straw  in  the  mouth. 
If  the  piston  in  the  tube  in  the  illus-    AlR  PRESSUEE  FORCES 
tration  were  pushed  down,  the  water     THE  WATER  UP  THE 
also   would   flow   down.     This   return 
flow  of  the  water  is  prevented  in  the  common  pump  by 
placing  valves  in  the  tube.     The  valves  open  when  the 
water  flows  up  but  close  when  it  tries  to  flow  down. 

In  common  lifting  pumps  there  is  a  valve  in  the  piston 
and  one  in  the  pump  tube  as  shown  in  the  illustrations  on 
page  215.  When  the  piston  moves  down,  the  valve  in  it 
opens  and  the  air  escapes,  as  in  diagram  i,  while  the  valve 
in  the  pump  tube  was  closed  by  its  own  weight  and  by 
the  force  of  the  air  trying  to  pass  through.  In  diagram 
2  the  piston  is  rising  and  the  valve  in  it  was  closed  by  the 


WATER   OR   LIQUID    PUMPS 


215 


air  pressure;  hence  the  air  is  prevented  from  getting  back 
into  the  pump,  while  the  air  and  water  below  the  valve 
in  the  pump  tube  open  the  valve  and  fill  the  space  below 


Air  tight 


Valve  -3^M 


THE  COMMON  PUMP 

the  piston  with  air  and  water.  In  diagram  3  the  valve  in 
the  pump  tube  closed  to  prevent  the  return  of  the  water 
to  the  well,  while  the  valve  in  the  piston  opened  and 
allows  the  water  to  flow  above  it  as  the  piston  descends. 
At  the  next  upward  stroke  of  the  piston  the  water  will  be 


2l6 


GENERAL  SCIENCE 


lifted  out  of  the  pump.  The  air  pressure  on  the  water  in 
the  well  is  what  forces  the  water  up  through  the  first 
valve  of  the  pump,  but  it  will  do  this  only  when  the  air 
pressure  in  the  pump  is  reduced  by  the  upward  move- 
ment of  the  piston.  The  piston  must  always  be  placed 
less  than  34  feet  from  the  surface  of  the  water  in  a  well. 

Lift  pumps  are  used  in  wells  that  are  not  very  deep 
and  in  places  where  it  is  not  desired  to  pump  the  water 
very  far.  The  quantity  of  water  thrown  depends  upon 
the  size  of  the  pump  and  the  speed  at  which  the  piston 
moves  up  and  down.  The  piston  is  usually  placed  down 
in  the  well  far  enough  to  prevent  freezing. 

147.  The  Force  Pump.  —  The  top  of  a  common  lift 
pump  is  not  water-tight,  and  so  water  cannot  be  raised 
any  higher  than  the  pump,  even  if 
a  hose  is  placed  on  the  pump  spout. 
If  the  top  were  made  water-tight, 
water  could  be  forced  through  a 
hose  attached  to  the  spout,  and  the 
pump  would  then  be  a  force  pump. 
Force  pumps  are  usually  made  so 
that  the  downward  stroke  of  the 
piston  forces  the  water  out.  This  is 
done  by  placing  the  second  valve  in 
the  side  of  the  cylinder  rather  than 
in  the  piston.  In  the  illustration, 
the  valve  V  closes  when  the  piston 
goes  up,  and  the  valve  D  opens  to  permit  water  to  flow 
in  from  the  well.  When  the  piston  descends  the  valve 
D  is  closed  by  the  pressure  of  the  water  on  it,  and  the 
valve  V  is  forced  open  and  the  water  flows  out  through 
the  delivery  pipe.  The  weight  of  the  water  in  the 
delivery  pipe  closes  the  valve  V  when  the  piston 


FORCE  PUMP 


WATER   OR  LIQUID    PUMPS 


217 


ascends,  so  there  is  only  an  intermittent  flow  of  water 
from  the  spout  or  hose  attached  to  such  a  force  pump. 

In  order  to  avoid  this  intermittent  dis- 
charge and  have  a  steady  stream,  an  air 
dome  or  chamber  must  be  attached  to  the 
delivery  tube,  as  shown  in  the  illustration. 
The  downward  movement  of  the  piston 
forces  water  through  the  delivery  tube  and 
also  into  the  air  dome,  because  air  can  be 
easily  compressed.  (If  air  is  compressed 
to  one-third  its  original  volume,  it  exerts  a 
pressure  three  times  as  great  as  before.) 


FORCE  PUMP 
WITH  AIR  DOME 


So   when   the    piston    again    ascends,   the 

valve  V  closes,  but  the  compressed  air  in  the  air  dome 


AIR  DOMES  or  HIGH  PRESSURE  PUMPS 

From  photograph  of  those  used  for  pumping  the  water  to  wash  the 
sand  of  the  niters  of  the  Pittsburgh  city  water. 

forces  the  water  out  of  the  delivery  tube  and  keeps  the 
stream  of  water  flowing  until  the  next  downward  stroke 
of  the  piston,  when  the  dome  is  again  filled.  In  this 
way  a  continuous  flow  is  obtained.  The  size  of  the  air 


2i8  GENERAL  SCIENCE 

dome  is  determined  by  the  size  of  the  pump.  The 
distance  that  water  can  be  thrown  depends  upon  the 
force  applied  to  the  piston. 

Force  pumps  are  often  used  in  wells,  and  especially 
when  a  windmill  is  used  as  power  for  pumping.  City 
fire  engines  which  force  water  to  the  tops  of  high  build- 
ings use  the  force  pump  with  a  very  large  air  dome. 
City  water  companies  use  high  pressure  force  pumps 
to  pump  water  into  standpipes  and  hilltop  reservoirs. 
Force  pumps  are  also  used  for  spraying  fruit  trees  and 
other  vegetation. 

148.  The  Centrifugal  Pump  is  a  very  modern  type  of 
pump  without  a  piston  or  valve  in  the  pump  chamber. 

It  consists  of  a  wheel 
enclosed  in  a  strong 
metal  case.  The  wheel 
is  made  to  rotate  very 
rapidly,  and  curved, 
spoke-like  parts  throw 
the  water  to  the  outer 
>UMP  part  of  the  wheel  and 

case,  and  it  is  thus  forced  through  the  pipe  or  tube 
which  leads  from  the  case.  As  the  wheel  rotates  rapidly 
a  partial  vacuum  is  produced  in  the  case,  and  the  air 
pressure  on  the  water  in  the  river  or  other  source  of 
supply  forces  the  water  through  a  tube  to  the  center  of 
the  rotating  wheel.  The  wheel  forces  it  to  the  outer  cir- 
cumference of  the  case  and  out  through  the  delivery  tube. 
The  quantity  of  water  delivered  by  such  a  pump  is 
dependent  upon  the  size  and  speed  of  the  wheel.  The 
centrifugal  pump  is  not  a  high-pressure  pump,  and  it  is 
used  only  where  it  is  not  necessary  to  raise  the  water 
many  feet  and  where  a  large  quantity  of  water  is  desired. 


WATER   OR   LIQUID    PUMPS  219 

Much  of  the  water  used  for  irrigating  arid  lands  is  ele- 
vated a  few  feet  for  that  purpose  by  centrifugal  pumps. 
When  caissons  of  any  kind  are  sunk  in  a  river  for  con- 
struction work,  such  as  the  building  of  abutments  for 
bridges  or  laying  pipe  lines  across  a  river,  the  centrifugal 
pump  is  used  to  remove  the  water.  Swamp  lands  also 
can  easily  be  drained  by  this  pump.  Sand  and  other 


*&*  ••      \ 


LARGEST  CENTRIFUGAL  PUMP  IN  THE  WORLD 
It  can  deliver  100,000,000  gallons  in  24  hours.    (Pittsburgh  City  Water.) 

foreign  matter  do  not  injure  the  centrifugal  pump  as 
they  do  the  valves  of  the  force  or  lift-pump. 

149.  Wells  and  How  to  Get  Water  from  Them.  —  Wells 
are  sometimes  made  by  digging  a  round  hole  about  six 
feet  in  diameter  and  deep  enough  to  reach  sufficient 
water.  The  well  is  then  walled  with  stone,  leaving  an 
opening  in  the  center  about  three  feet  in  diameter.  The 
water  usually  comes  from  an  underground  stream  called 
a  vein.  Wells  sixty  or  more  feet  deep  are  drilled  by 
machinery,  and  a  large  pipe  casing  is  put  down  for  the 
wall.  Wells  which  are  not  very  deep  are  usually  drilled, 


220 


GENERAL   SCIENCE 


because  this  is  not  so  expensive  as  digging.  In  sandy 
places  where  the  water  is  known  to  be  near  the  surface, 
sharp-pointed  pipes  with  a  number  of 
small  holes  near  the  pointed  end  are 
driven  down  until  they  reach  the  water. 
A  common  pump  is  then  put  in  the  pipe 
and  water  can  be  obtained. 

In  all  wells  the  piston  of  the  pump  must 
be  within  34  feet  of  the  water,  or  the  air 
pressure  will  not  raise  the  water  to  the 
first  valve.  Since  the  valves  cannot  be 
made  perfectly  air-tight,  the  pump  will 
work  better  if  the  piston  is  not  more  than 
20  or  25  feet  from  the  surface  of  the  water. 
Force  pumps  are  used  in  deep  wells  be- 
cause the  piston  can  be  placed  low  and 
the  water  forced  from  the  piston  to  the 

top.     Even   in   a   common   lifting  pump 
FORCE  PUMP  WITH  ,  *          .  ,        .        ,  ,   .. 

PISTON  IN  WATER  the  Plst°n  1S  Placed  several  ieet  d°wn  in 
the  well  in  order  to  make  it  easier  for  the 
air  to  force  the  water  up  to  it,  and  also  to  prevent 
freezing  in  winter.  Freezing  is  prevented  by  opening  a 
valve  just  above  the  piston,  which  permits  the  water 
above  the  piston  to  flow  out  of  the  tube.  This  valve 
must  be  closed  again  when  one  wants  to  pump  water. 

QUESTIONS    AND    EXERCISES 

1.  How  does  the  air  aid  one  in  drinking  a  liquid  through  a  straw  ? 

2.  Make  a  siphon  of  a  rubber  hose  and  explain  the  cause  of 
the  flow  of  the  liquid. 

3.  Explain  the  difference  between  a  common  lifting  pump  and 
a  force  pump. 

4.  Why  do  high-pressure  force  pumps  have  air  domes  ? 

5.  When  ought  you  to  install  a  centrifugal  pump  rather  than 
a  force  pump  ? 


CHAPTER  XXIII 
GAS  PUMPS 

150.  Gas  Pumps  are  used  principally  for  pumping  air. 
The  structure  of  the  gas  pump  is  different  from  that  of 
the  liquid  pump.     The  valves  are  different,  and  to  be  air- 
tight they  must  fit  more  accurately  than  to  be  merely 
water-tight.     In   cheap    pumps   the   valves   are   usually 
made  of  leather  and  are  kept  soft  and  flexible  by  lubri- 
cating oil.     Since  the  molecules  of  air  are  moving  very 
rapidly,  it  will  expand  when  the  pressure  on  it  is  reduced. 
On  this  account  air  can  be  pumped  into  or  out  of  a  vessel. 
To  pump  air  into  a  vessel  the  valve  on  the  piston  must 
be  turned  in  the  opposite  direction  from  that  in  a  pump 
that  will  force  air  out  of  a  vessel;   the  former  is  called  a 
compression  pump  and  the  latter  an  exhaust  pump. 

151.  The     Compression     Pump.  —  The     compression 
pump  is  one  with  which  air  can  be  compressed  or  forced 
into   a  vessel  or  bicycle   tire.     The  diagram 
illustrates  the  action  of  a  compression  pump. 

When  the  piston  is  forced  down,  the  valve 
V  rubs  against  the  side  of  the  pump  tube 
and  prevents  the  air  from  escaping  above  or 
around  the  piston,  and  so  the  air  is  forced 
through  the  rubber  tube  into  the  tire.  While 

the  piston  was  going  downward,  the  pump 

'     ,  ,          .  ,     .         -,,    -,       .,,      COMPRESSION 

tube  above  the  piston  was  being  filled  with         puMp 

air  which  passed  in  through  the  opening  0. 
Some  pumps  permit  the  air  to  pass  in  through  the  open- 
ing around  the  piston  bar.     When  the  piston  is  drawn 


o 


222  GENERAL  SCIENCE 

upward,  the  valve  in  the  tire  closes  and  prevents  the 
escape  of  the  air  from  it.  The  valve  V  bends  downward 
and  allows  the  air  above  it  to  flow  below  the  piston. 
This  air  is  driven  into  the  tire  at  the  next  downward 
stroke. 

Compression   pumps    have    a    very    wide    commercial 
use.     Every  locomotive  and  street  car  has  a  compression 
pump   which   supplies   the   compressed   air   for   the   air- 
brakes;  the  self-opening  and  self-closing  doors  on  electric 
cars  are  also  moved  in  this  way.     Compression  pumps 
are  sometimes  used  for  ventilating  mines  so  that  gases 
and  impure  air  cannot  collect  in  them;    but  two  rotary 
fans  are  more  often  used  for  mine  ven- 
tilation,  similar  to  those  used  for  ven- 
tilating   large    buildings    and    factories. 
One  fan  forces   air  into  the  mine  and 
the  other   removes  it.     Compressed   air 
drills  used  in  stone  quarries  and  com- 
pressed  air    riveters   used    in    the    con- 
Am  KEEPS         struction    of    modern     skyscrapers    are 
WATER    OUT         very   valuable    commercial    tools   made 

possible  by  the  compression  pump. 
The  compression  pump  has  made  it  possible  for  man 
to  work  under  water.  To  illustrate  how  this  is  done, 
place  a  glass  tube  in  water  and  blow  into  one  end  of  it. 
As  the  air  enters,  the  water  moves  out,  showing  that  air 
can  hold  water  out  of  a  vessel  when  the  vessel  is  immersed 
in  water.  A  diving-bell  large  enough  for  men  to  work  in 
can  be  sunk  from  a  boat  and  air  pumped  into  it  to  keep 
out  the  water;  this  air  also  supplies  oxygen  to  the  men. 
Excavations  for  bridge  piers  in  deep  water  are  sometimes 
made  by  sinking  an  air-tight  caisson  and  then  keeping 
the  water  out  of  the  place  where  the  men  work  by  com- 


GAS   PUMPS 


223 


pressed  air.  Men  can  also  work  under  water  by  using 
diving  suits  all  made  of  rubber  except  the  head  protector, 
which  is  made  of  metal  with  transparent  eyepieces. 
Some  divers  carry  a  tank  of  compressed 
air  to  breathe  and  others  have  air  pumped 
to  them  through  a  tube. 

Men  cannot  work  under  water  very  long 
because  it  is  difficult  to  adjust  themselves 
to  the  high  pressure  which  is  necessary  to 
keep  the  water  out.  Divers  scarcely  ever 
work  at  a  depth  greater  than  60  feet,  and 
80  feet  or  90  feet  is  usually  considered  the 
limit  of  safety.  But  while  building  the 
bridge  across  the  Mississippi  at  St.  Louis, 
Missouri,  the  diving-bells  with  the  work- 
men were  sunk  to  a  depth  of  no  feet.  A 
case  is  on  record  of  a  diver  who  sank  to 
a  depth  of  201  feet  while  he  was  investi- 
gating a  wreck  off  the  coast  of  South  America. 

The  diver  experiences  pain  in  his  ears  and  above  the 
eyes  while  he  is  descending  and  ascending,  but  he  feels 
no  pain  when  at  rest.  This  is  because  it  takes  some 
time  for  the  air  to  enter  the  interior  parts  of  the  body 
and  establish  a  pressure  on  the  inside  equal  to  that  on 
the  outside. 

152.  The  Exhaust  Pump.  —  In  the  exhaust  pump  the 
valves  are  the  reverse  of  those  in  the  compression  pump. 
Air  can  be  pumped  from  a  vessel  because  it  will  expand 
and  fill  the  entire  vessel  regardless  of  how  much  air  is  in 
it.  When  the  piston  of  the  pump  in  the  illustration 
moves  upward,  the  air  in  the  vessel  Af,  to  which  the 
pump  is  attached,  expands  and  fills  the  pump  tube  below 
the  piston;  at  the  same  time  the  air  above  the  piston  is 


DIVING  SUIT 


224 


GENERAL  SCIENCE 


EXHAUST  PUMP 


being  forced  out.  When  the  piston  moves  downward 
the  valve  D  closes  and  does  not  permit  any  air  to  enter, 
while  the  air  below  the  piston  passes  around  the  piston 
valve  V  and  fills  the  pump  tube  above  the  piston.  At 
each  upward  stroke  a  pump  full  of 
rarefied  air  is  taken  from  the  vessel. 
The  commercial  use  of  the  ex- 
haust  pump  is  not  so  extensive  as 
that  of  the  compression  pump,  al- 
though very  necessary.  Electric 
light  bulbs  have  the  air  removed 
so  that  oxygen  cannot  burn  the 
filament.  Thermos  bottles  have  the 
air  removed  from  between  the  two 
glass  bottles  so  that  heat  cannot 
pass  out  by  conduction  or  convection. 
153.  Pneumatic  Dispatch  Tubes  used  in  department 
stores,  railroad  stations,  and  in  many  cities  for  sending 
mail,  have  an  exhaust  pump  at  one  end  to  remove  air 
from  the  tube.  The  articles  sent  through  the  tubes  are 
placed  in  leather  cases  which  fit  tight  in  the  metal  tube 
so  that  the  air  cannot  pass  around  them.  The  exhaust 
pump  removes  the  air  pressure  from  in  front  of  the 
leather  case,  and  the  compressed  air  behind  it  forces 
the  case  rapidly  through  the  tube. 

QUESTIONS    AND    EXERCISES 

1.  Take  the  valve  out  of  a  bicycle  pump  and  explain  its  action. 

2.  Is  the  bicycle  pump  a  compression  pump  or  a  force  pump  ? 

3.  How  does  a  compression  pump  differ  from  an  exhaust  pump  ? 

4.  What  practical  use  is  made  of  both  kinds  of  pumps  ? 
0.  Which  kind  do  you  think  is  used  more  extensively  ? 


CHAPTER  XXIV 
CITY   WATER   SUPPLY 

154.  The  Problem  of  Pure  Water.  —  The  problem  of 
supplying  rapidly  growing  American  cities  with  water  is 
not  an  easy  one  and  to  supply  pure  water  is  much  more 
difficult.  The  city  of  New  York  has  spent  many  millions 
of  dollars  to  bring  a  supply  of  pure  water  from  the  Cats- 
kill  Mountains.  Pittsburgh  has  one  filtering  plant  that 
covers  60  acres  and  has  spent  a  large  sum  during  the  last 
ten  years  to  get  pure  water.  Many  other  cities  are  doing 
the  same.  The  world  has  awakened  to  the  necessity  of 
pure  water,  principally  because  of  the  large  number  of 
epidemics  of  typhoid  fever  which  have  been  caused  by 
contaminated  water.  Typhoid  fever  germs  live  in  the 
food  tube  of  the  body  and  the  excreta  of  a  typhoid  patient 
contain  large  numbers  of  such  germs.  In  a  city  with  a 
system  of  sewage  such  germs  might  pass  from  the  sewers 
into  a  river  without  being  killed.  Some  cities  and 
towns  take  their  water  directly  from  rivers,  at  times  not 
far  below  another  large  city.  Such  cities  will  get  many 
germs  in  their  water  supply.  Other  cities  —  as  Buffalo 
and  Cleveland — take  their  water  from  lakes  into  which 
their  own  sewage  flows.  Many  cities  which  drain  their 
sewage  into  rivers  and  lakes  now  have  a  means  of  dis- 
posing of  the  sewage  in  such  a  way  as  to  render  it  harmless 
to  their  neighbor  cities.  Filtering  river  water  by  passing 
it  through  settling  basins  and  sand  filters  and  adding 
chemicals  removes  about  98  per  cent  of  the  germs.  The 


226 


GENERAL  SCIENCE 


comparative  results  of  drinking  unaltered  and  filtered 
water  in  four  of  our  American  cities  is  shown  graphically 
in  the  diagram  below. 

155.  Methods  of  Purifying  Water.  —  (a)  Boiling  the 
water  will  kill  the  germs  in  it  but  will  not  take  out  any 
impurities.  Water  must  be  clean  enough  to  drink  before 
boiling,  except  for  a  few  living  germs,  or  it  will  not  be 
fit  for  drinking  after  boiling.  The  destruction  of  germs 
by  boiling  is  practicable  only  in  private  homes.  It 
would  be  too  expensive  for  the  city  water  supply. 


M     N  M     N  M     N  M     N 

BlNGHAMTON,  N.  Y.       WATERTOWN,  N.  Y.          ALBANY,  N.  Y.  LAWRENCE,  MASS. 

DIAGRAM  SHOWING  HOW  SUPPLYING  A  CITY  WITH  GOOD  WATER 
LESSENS  SICKNESS  AND  DEATH 

The  lines  M  above  each  city  show  the  relative  number  of  persons  dying 
of  typhoid  fever  before  the  water  was  filtered.  The  lines  N  show  the  num- 
ber dying  after  the  water  was  filtered.  The  figures  are  the  number  of  deaths 
from  typhoid  occurring  out  of  100,000  inhabitants. 

(b)  Distilling  is  the  most  effective  method  of  purifica- 
tion.    It  removes  from  the  water  not  only  disease  germs 
but  also  many  other  impurities,  such  as  dissolved  salts. 
Artificial  ice  is  made  of  distilled  water  and  hence  it  is 
free  from  germs.     But  distillation  would  be  a  very  ex- 
pensive method  of  purifying  water  for  cities. 

(c)  Filtering  with  the  aid  of  a  few  chemicals  is  the 
method  used  for  purifying  city  water.     The  filter  bed  is 


CITY    WATER    SUPPLY 


227 


made  of  two  or  three  feet  of  fine  sand  spread  on  top  of  a 
foot  or  two  of  coarse  sand  and  gravel,  with  stones  at 
the  bottom.  As  the  water  soaks  through  the  sand  the 
solid  matter  —  the  impurities  —  are  left  on  top  of  the 
filter  bed.  The  filter  bed  is  underlaid  with  piping  full 
of  holes  to  receive  the  filtered  water. 


INTERIOR  OF  FILTERING  PLANT 
Showing  the  instruments  for  operating  each  filter.     (Penn'a  Water  Co.) 

In  the  slow  filtering  process  the  water  is  pumped  to  a 
settling  basin  in  which  the  heavy  sediment  sinks  to  the 
bottom.  From  the  settling  basin  it  is  permitted  to 
flow  slowly  on  the  filter  beds.  For  a  large  city  there 
must  be  several  acres  of  filter  beds.  From  the  filters  the 
water  flows  into  a  storage  basin  where  enough  chemicals 
are  added  to  kill  the  disease  germs. 

In  the  rapid  filtering  process  the  water  is  pumped 
from  the  river  to  the  top  of  a  high  hill  where  the 
filtering  plant  is  located.  The  amount  of  chemicals 


228  GENERAL  SCIENCE 

necessary  to  precipitate  solid  matter  and  kill  bacteria 
and  germs  is  put  into  the  water  just  before  it  pours  from 
the  pump  delivery  pipes  into  the  settling  basin.  From 
the  settling  basin  it  flows  over  the  filter  beds,  which  are 
about  20  feet  long  and  18  feet  wide.  Each  filter  bed 
will  remove  the  solid  matter  and  dead  germs  from  about 
1,000,000  gallons  in  24  hours.  These  filter  beds  are 
washed  once  every  24  hours  by  forcing  water  through 
them  in  the  opposite  direction  from  that  in  which  the 
filtering  water  flows  through. 

156.  Methods  of  Supplying  Water.  —  Cities  have  vari- 
ous methods  of  supplying  sufficient  water  for  their  needs, 
depending  upon  their  location  with  regard  to  streams, 
lakes,  and  mountains.  There  are  three  systems  in  use. 

(A)  Gravity   System.  —  Cities    that    are    located    near 
mountains  have  the  water  piped  from  lakes  or  streams 
that  have  an  elevation  much  greater  than  that  of  the  cities. 
In  this  way  great  pressure  is  secured  for  the  entire  city, 
and  the  water  will  flow  with  considerable  force  from  any 
faucet.     The  water  flows  to  the  city  because  of  its  own 
weight.     Denver,  Colorado,  uses  the  gravity  system  by 
having   the   water   piped   from    the   mountain   streams. 
Los  Angeles,   California,   is  using   this   system  in  part. 
The  water  from  the  mountains  is  usually  pure  enough 
so  that  it  does  not  need  to  be  filtered,  and  the  expense 
of  both  pumping  and  filtering  is  avoided. 

(B)  The  Pumping  System  is  used  extensively  by  small 
cities  along  rivers  and  in  those  parts  of  the  country  in 
which  there  are  no  elevations  or  hills  upon  which  to  place 
reservoirs  or  stand  pipes.    In  some  Western  cities  the 
water  is  filtered  and  then  pumped  through  the  main  pipe 
lines  into  the  houses.     In  certain  cities  along  the  Ohio 
River  the  water  is  pumped  directly  into  the  houses  with- 


CITY   WATER    SUPPLY 


229 


out  being  filtered.  The  speed  of  the  pumps  is  deter- 
mined by  the  pressure  of  the  water  in  the  main  pipes. 
When  a  great  number 
of  people  are  using  water 
the  pressure  in  the  pipes 
is  slightly  reduced  and 
the  pumps  then  increase 
their  speed,  thus  keep- 
ing the  pressure  about 
constant. 

(C)  Combination  of 
the  Pumping  and  Gravity 
Systems.  —  Cities  located 
in  hilly  parts  of  the 
country  use  the  tops  of 
some  of  the  hills  for 
storage  reservoirs  for  water.  Standpipes  also  are  usu- 
ally located  on  some  high  point.  The  water  is  pumped 
from  wells  or  rivers  into  these  reservoirs  or  standpipes 


FILTERING  PLANT  AND  STANDPIPE 


SETTLING  BASIN 

Water  coming  from  the  river  560  feet  below.     The  chemicals  are  added 
before  the  water  comes  out  of  these  fountains.     (Penn'a  Water  Co.) 

and  then  it  is  permitted  to  flow  through  the  mains  into 
the  houses  by  the  force  of  its  weight  or  gravity;   thus 


230 


GENERAL   SCIENCE 


the  pumps  force  it  to  the  reservoirs  and  gravity  delivers 
it  to  the  houses.  New  York  City  uses  gravity  to  deliver 
the  water  from  the  Catskills,  but  after  reaching  the  city 
the  water  has  to  be  pumped  in  order  to  have  sufficient 
pressure. 

157.   Why  Water  Pressure  is  not  Uniform.  —  Before 
city    reservoirs    and    standpipes    are    constructed,    it    is 


RESERVOIR  AND  STANDPIPE 

Standpipes  used  with  the  reservoir  to  keep  a  constant  pressure  at  a 
distance  from  the  reservoir. 

necessary  to  ascertain  the  quantity  of  water  needed  in 
order  to  determine  how  strong  to  make  the  walls  of  the 
reservoirs  and  standpipes.  The  greater  the  height  at 
which  the  water  stands,  the  thicker  the  walls  must  be. 
The  greater  the  elevation  of  the  houses 
that  use  the  water,  the  stronger  must 
.  be  the  pumps  and  the  stronger  must  be 
the  walls  of  the  standpipe  to  resist  the 
pressure. 

In  order  to  understand  how  much 
pressure  water  in  a  reservoir  or  stand- 
pipe  has,  it  is  necessary  to  know  the 
weight  of  a  cubic  foot  of  water  and  the 
Cubic  foot  of  water  pressure  produced  by  water  which  is  a 
foot  deep.  A  cubic  foot  of  water 


i  root 
CUBIC  FOOT 


weighs  62.5  pounds. 


at  o  C.  weighs  about  62.5  pounds;  that  is,  when  water 
is  one  foot  deep  it  presses  down  62.5  pounds  on  every 
square  foot,  or  .434  of  a  pound  on  each  square  inch;  or 


CITY   WATER    SUPPLY 


231 


the  pressure  is  .434  of  a  pound  per  square  inch  for  each 
foot  in  depth.  If  the  water  is  10  feet  deep  the  pressure 
is  .434  X  10,  or  4.34  pounds  per  square  inch;  if  it  is  30 
feet  deep  the  pressure  is  13.02 
pounds  per  square  inch  on  the  bot- 
tom of  the  vessel  or  reservoir. 
Standpipes  100  feet  high  full  of 
water  have  a  pressure  of  43.4 
pounds  per  square  inch  at  the 
bottom. 

The  pressure  against  the  side  of 
the  standpipe  near  the  bottom  is 
almost  the  same  as  the  pressure  on 
the  bottom.     The  pressure  against 
the  side  of  the  standpipe  halfway 
up  is  half  the  pressure  at  the  bot- 
tom.    If  the  standpipe  were  tapped  at  the  bottom  and 
also  halfway  up  from  the  bottom,  the  water  would  flow 
out  with  a  force   twice  as  great  at   the  bottom  as  it 
would  at  the  upper  spout.     If  the  standpipe  is  only  half 


HEIGHT  OF  WATER  DE- 
TERMINES THE  PRESSURE 


PUMPING  SYSTEM 
Used  in  level  countries,  assisted  by  standpipes. 

full,  the  water  pressure  at  the  bottom  is  only  one-half  as 
great  as  when  it  is  full  to  the  top.  From  this  we  see  that 
if  the  height  of  the  water  in  the  standpipe  varies,  the 
pressure  in  the  pipes  leading  from  it  to  the  houses  will 


232  GENERAL  SCIENCE 

also  vary.  As  the  height  of  water  in  the  reservoir  changes, 
the  pressure  in  the  houses  will  also  change. 

Water  pressure  is  also  reduced  by  the  friction  of  the 
flow  of  the  water  through  the  pipes,  joints,  and  valves. 
Again,  if  many  people  are  using  water  at  the  same  time, 
the  pressure  will  be  lessened  because  the  pipes  are  not 
usually  large  enough  to  carry  a  full  pressure  supply  for 
all  at  the  same  time.  So  the  three  conditions  upon  which 
water  pressure  is  dependent  are  the  height  of  water  in 
the  reservoir,  friction  in  the  pipes,  and  the  number  of 
people  using  water  at  one  time.  If  several  people  on 
the  first  floor  of  a  building  are  drawing  water,  those 
on  the  upper  floors  may  not  get  any,  as  trie  pipes  in  the 
basement  are  not  usually  large  enough  to  carry  sufficient 
water  to  make  it  flow  from  all  the  faucets  at  the  same 
time. 

158.  Equal  Pressure.  —  Large  cities  try  to  meet  the 
difficulties  discussed  in  §  157  by  having  reservoirs  on 
various  hilltops;  or  if  hills  are  not  sufficiently  numerous, 
standpipes  are  erected  at  various  distances  from  the 
reservoir,  or  pumping  station.  If  there  are  a  number  of 
reservoirs,  the  friction  caused  by  water  flowing  through 
long  pipes  is  avoided  and  a  more  constant  pressure  and 
supply  are  secured.  If  the  reservoir  and  standpipe 
system  is  used,  the  water  flows  from  the  reservoir  into 
the  standpipe  when  not  many  people  are  drawing  water. 
During  the  hours  when  a  large  quantity  of  water  is 
needed,  it  flows  from  the  standpipe  because  the  distance 
of  flow  is  less  and  hence  the  friction  is  not  so  great  as  when 
the  water  flows  from  the  distant  reservoir.  Standpipes 
are  also  often  combined  with  the  pumping  system  in  order 
to  insure  normal  pressure  in  the  parts  of  the  city  which 
are  distant  from  the  pumping  station. 


CITY   WATER   SUPPLY  233 

159.  The  Cost  of  City  Water.  —  Families  may  have 
to  pay  from  one  dollar  to  ten  dollars  per  year  for  water. 
This  is  not  very  much  per  gallon,  but  when  the  total  cost 
of  a  large  city  is  ascertained  it  amounts  to  millions  of 
dollars.     Where  the  gravity  system  is  used  the  cost  is 
very  small,  as  not  much  work  is  needed  after  the  pipes 
are  once  laid.     But  where  the  cities  are  in  a  level  country, 
or  where  the  source  of  water  is  no  higher  than  the  city, 
the  cost  of  water  is  greater  because  of  the  necessity  of 
pumping  it  and  often  of  purifying  it. 

To  get  some  idea  of  the  work  done  in  pumping  water 
for  a  city,  let  us  consider  the  Pennsylvania  Water  Co., 
which  supplies  water  to  about  30,000  people,  principally 
in  Wilkinsburg,  Pa.  A  gallon  of  water  weighs  approxi- 
mately 8.3  pounds.  The  work  done  by  a  pump  in  raising 
a  gallon  of  water  560  feet  to  the  filtering  plant  is  8.3  X 
560,  or  4,648  foot  pounds.  The  company  pumps  8,000,- 
ooo  gallons  every  24  hours,  and  the  work  done  in  raising 
it  to  the  filtering  plant  is  8.3  X  560  X  8,000,000,  or 
37,184,000,000  foot  pounds.  The  work  that  can  be 
done  by  one  horse  power  in  24  hours  is  550  X  60  X  60  X 
24,  or  47,520,000  foot  pounds.  So  the  number  of  horse 
power  required  to  pump  that  water  is  approximately 
37,184,000,000  -4-  47,520,000,  or  782  H.  P.  An  engine 
of  about  1,000  H.  P.  would  be  required  to  pump  the 
8,000,000  gallons  per  day  up  to  the  filtering  plant.  After 
the  water  is  filtered,  it  is  destributed  by  the  force  of 
gravity  to  the  various  houses  in  the  valley  below. 

160.  Water    Supply    and    Forests.  —  There    are    two 
causes  which  influence  the  maximum  flood  stage  of  most 
streams. 

First.  The  highest  floods  usually  come  when  a  heavy 
snow  is  melted  by  a  warm  rain  during  the  winter  or  early 


234  GENERAL  SCIENCE 

spring.  Now  as  a  rule  forests  give  the  snow  some  pro- 
tection from  the  direct  rays  of  the  sun  and  so  delay  its 
melting;  but  this  snow  will  go  off  rapidly  when  a  warm 
rainy  season  comes.  The  snow  water  and  rain  usually 
give  the  river  channels  more  water  than  they  can  carry 
and  a  flood  results.  Where  there  are  no  forests  the  snow 
on  the  southern  slopes  is  usually  melted  by  the  direct 
rays  of  the  sun,  and  the  water  from  it  is  gone  and  out  of 
the  way  before  the  snow  on  the  northern  slopes  is  melted 
directly  by  the  sun  or  by  warm  rains.  The  snow  on  the 
eastern  and  western  slopes  will  melt  gradually  between 
the  melting  of  that  on  the  southern  and  northern  slopes 
where  there  is  no  forest.  A  flood  caused  by  the  melting 
of  snow  by  rain  is  general  and  affects  the  large  rivers  as 
well  as  the  small  streams.  This  first  cause  is  in  favor  of 
the  deforested,  region  or  sections  and  against  the  forests. 
Second.  The  second  cause  is  in  favor  of  the  forested 
regions.  By  careless  methods  of  agriculture  many 
deforested  fields  and  slopes  are  unprotected  by  any  kind 
of  vegetation.  This  bare,  wornout  soil,  having  lost 
its  ability  to  receive  and  retain  water  because  of  the  loss 
of  its  humus,  does  not  permit  much  of  the  water  to  soak 
down  into  it,  and  so  the  water  rushes  rapidly  down  the 
slopes  and  into  the  larger  streams,  carrying  a  large 
quantity  of  sediment,  clay,  sand,  and  rock.  The  larger 
creeks  that  do  not  flow  so  rapidly  are  not  able  to  transport 
the  heavy  load  of  solid  matter  delivered  to  them,  and 
so  their  beds  become  choked  with  gravel  and  rock.  A 
creek  bed  almost  full  of  sediment  does  not  require  much 
water  to  fill  it,  and  the  result  is  that  the  excess  of  water 
during  a  rainy  season  is  spread  over  the  valley  on  either 
side.  These  creeks  during  their  flood  stages  deliver  more 
sediment  to  the  rivers  than  they  are  able  to  move  along, 


CITY    WATER    SUPPLY  235 

and  their  beds  become  filled.  The  levees  along  the  Ohio 
and  Mississippi  must  be  continually  raised  in  order  to 
keep  the  water  within  the  river  banks.  The  bed  of  the 
Mississippi  is  in  many  places  higher  than  the  country  on 
either  side;  hence  when  the  water  breaks  through  its  levee 
much  damage  is  done. 

If  our  rural  population  would  learn  how  to  keep  the 
cleared  fields  covered  with  vegetation  and  the  soil  supplied 
with  the  proper  amount  of  humus, -this  cause  of  floods 
would  be  removed,  and  there  would  be  less  need  of  the 
forests  so  far  as  the  control  of  water  supply  is  concerned. 
There  are,  however,  many  good  reasons  why  there  should 
be  forest  regions  and  wooded  slopes. 

The  soil  in  the  woods  during  a  long  dry  season  is  much 
dryer  than  the  soil  in  a  properly  cultivated  field.  A 
grass  field  is  also  much  dryer  than  a  field  under  cultiva- 
tion. The  reason  is  that  the  roots  of  the  trees  absorb 
the  water  from  the  soil  rapidly  and  it  is  transported  to 
the  leaves,  which  give  it  to  the  air  by  evaporation.  Water 
from  the  deeper  parts  of  the  earth  gradually  works  its 
way  to  the  surface  during  a  dry  season,  but  the  roots  of 
the  trees  absorb  it  as  fast  as  it  comes  by  capillarity 
toward  the  surface.  In  a  cultivated  field  where  crops 
are  growing,  the  leaf  surface  of  the  plants  is  not  nearly 
so  great  as  the  area  of  all  the  leaves  on  the  trees  in  the 
woods,  and  for  this  reason  there  is  not  so  much  water 
given  off  by  evaporation  by  the  cultivated  crop  as  there 
is  by  the  forest  trees.  Evaporation  from  the  bare  soil  is 
also  prevented  by  stirring  the  surface  of  the  soil  and  pro- 
ducing what  is  known  as  dust  mulch.  Farmers  who  have 
not  learned  how  to  conserve  soil  moisture  during  dry 
seasons  do  not  have  much  success  in  agriculture. 

From  this  comparison  it  can  easily  be  seen  that  during 


236  GENERAL  SCIENCE 

a  dry  season  there  will  be  more  water  to  flow  into  the 
creeks  or  rivers  from  properly  cultivated  fields  than  from 
forested  regions,  and  when  rain  comes  the  cultivated  fields 
will  be  moistened  sooner  than  the  forested  parts  and  so 
the  streams  will  again  receive  water  from  the  cultivated 
fields  before  they  will  from  the  woods. 

There  is  practically  no  effect  upon  the  rainfall,  floods, 
or  water  supply  when  a  forested  region  is  changed  to  a 
properly  cultivated  agricultural  section.  Careless  farm- 
ing, of  course,  results  in  the  loss  of  much  that  is  useful. 

QUESTIONS    AND    EXERCISES 

1.  What  is  the  source  of  water  for  your  home?      Is  it  free 
from  typhoid  or  other  disease  germs? 

2.  How  do  you  purify  your  drinking  water?     Do  you  use  the 
best  method? 

3.  Make  a  careful  study  of  water  supply  of  your  town  or 
city  in  order  to  learn  if  any  dangerous   chemicals  or  disease 
germs  are  in  it. 

4.  What  can  you  do  to  help  get  purer  water? 

5.  What  method  is  used  to  get  the  water  into  your  home? 

6.  Does  the  water  always  flow  with  the  same  force?     Why? 

7.  If  a  reservoir  is  150  feet  higher  than  your  home,  what  is 
the  water  pressure  at  the  spickets? 

8.  Determine  the  cost  per  gallon  of  water  which  you  use. 
(Obtain  the  necessary  facts  from  your  water  company.) 

9.  How  do  forests  affect  the  water  supply  of  your  locality? 

10.  Visit   some  creeks   to   see  if  they  have  been  affected  by 
the  removal  of  the  forests. 

11.  How  can  farmers  remedy  the  bad  effects  which  come  from 
the  removal  of  forests? 


CHAPTER  XXV 
MAGNETS 

161.  Natural  Magnet   or  Lodestone.  —  The   ancients 
found  a  certain  hard,  black  stone  at  Magnesia,  in  Asia 
Minor,  which  they  called  a  magnet.     It  had  the  property 
of  attracting  small  pieces  of  iron.     They  thought  that 
the  stone  possessed  some  magic  property  and  it  became 
very   famous.     It   was   not   discovered   until   about   the 
eleventh  century  that  the  famous  magnet-stone  would 
take  a  north  and  south  position  when  it  was  hung  up  by 
a  string.     This  property  of  the  stone  enabled  men  to 
determine  direction  by  its  aid,  hence  it  became  useful 
in  navigation.     From  such  uses  of  the  stone  it  received 
the    name    lodestone    or  "leading-stone."     The    natural 
magnet  is  an  iron  ore  called  magnetite,  which  has  the 
chemical  composition  FesCX,  an  iron  oxide.     The  ore  is 
found   in   quantities   in   Sweden,    Spain,   Arkansas,  .and 
other  parts  of  the  world,  but  not  always  in  a  magnetic 
condition. 

162.  Artificial  Magnet.  —  If  a  lodestone  is  rubbed  over 
a  piece  of  hard  iron,  the  iron  will  become  magnetized 
so  that  it  will  attract  particles  of  iron  in  the  same  way  as 
the  lodestone.     The  magnetized  iron  will  also  take  a  north 
and  south  position  when  it  is  suspended  by  a  thread. 
As   early  as    1729   it  was  learned   that  steel  will  hold 
magnetism  much  longer  than  iron. 

The  illustration  shows  that  the  iron  filings  adhere  in 
a  mass  at  the  ends  of  the  magnet  instead  of  covering 


238 


GENERAL   SCIENCE 


AN  ARTIFICIAL  MAGNET 
After  being  dipped  in  iron  filings. 


A  BAR  MAGNET 
MADE  or  STEEL 


it.     The  strings  of  filings   at  one   end   all  point  to  the 
same  part  of  the  magnet.     The  parts  to  which  the  filings 

point  are  the  poles  of  the 
magnet.  The  magnetic  force 
is  greatest  at  the  poles  and 
decreases  to  zero  toward  the 
middle  of  the  magnet.  The 
middle,  where  there  is  no  attraction,  is  called  the  equator, 
and  the  line  joining  the  two  poles  is  called  the  axis  of 
the  magnet.  In  a  horseshoe  magnet  the  equator  is  at 
the  curved  part,  the  poles  at  the  two  ends,  and  the  axis 
is  a  straight  line  joining  the  two  poles.  When  a  magnet 
is  suspended  so  that  it  can  swing 
freely,  the  end  pointing  north  is  called 
the  north-seeking  pole,  or  simply  the 
north  pole,  and  is  marked  N  on  the 
magnet;  the  other  end  is  called  the 
south  seeking,  or  south  pole,  and  is  indicated  by  S. 
A  compass  is  a  magnetized  steel  bar  balanced  on  a 
pointed  support  so  that  it  can  swing  freely  without  much 
friction.  It  is  shaped  so  that  one  can  tell  easily  in  what 
direction  it  points,  that  is,  tell  in  what  direction  the  axis 
stands.  When  a  compass  needle  is  free  to 
turn,  it  will  stand  with  its  axis  parallel  to 
the  magnetic  meridian.  The  compass  box 
has  the  directions  and  degrees  marked  so 
that  it  is  easy  to  tell  the  different  directions. 
163.  Magnetic  Attraction  and  Repulsion. 
-  There  is  no  visible  difference  in  the  way 
the  two  ends  of  a  bar  magnet  attract  iron 
filings.  But  there  is  a  difference  in  the 
two  poles,  which  can  be  seen  by  presenting  them  suc- 
cessively to  the  same  end  of  a  magnetic  needle.  One 


A  HORSESHOE 
MAGNET 


MAGNETS 


239 


MAGNETIC  ATTRACTION 
AND  REPULSION 


end  of  the  magnet  attracts  the  needle  and  the  other  end 

repels  it.     The  pole  of  the  magnet  which  repels  the  north 

pole  of  the  needle  attracts  the  south 

pole,  and  the  pole  of  the  magnet 

which   attracts   the   north   pole   of 

the   needle  repels   the   south  pole. 

From   this    we    conclude    that   the 

north-seeking  ends  of  magnets  repel 

each  other  and  a  north-seeking  end 

and    a    south-seeking    end    attract 

each  other,  that  is,  magnetic  poles 

of  like   kind   repel   each   other  and 

poles    of   unlike    kind    attract   each 

other. 

164.    Nature  of  Magnets.  —  No  magnet  can  be  made 

with  only  one  pole.     If  a  magnet  is  broken,  each  piece 

will  have  two  poles  of  opposite  kind.     The  poles  that 

appear  near  the 
point  of  break- 
ing are  of  oppo- 
site kind,  one  an 
N  pole,  the  other 
an  S  pole.  This 

subdivision  may  be  continued  indefinitely,  but  two  op- 
posite poles  will  appear  at  each  break. 

If  several  bar  magnets  are  laid  so  that  opposite  poles 

touch,    the    whole   line    of 

magnets    will    act   as    one     ^pjjjt  ^^^~^^~^^'^^ 

0  ^Z?//?/  ^^f^~ 

magnet  and  only  two  poles 

will  be  manifested,  one  at 

each  end.     Iron  filings  will 

adhere  in  quantity  only  around  these  two  poles.     The 

results  obtained  by  breaking  a  magnet,  and  by  placing 


WHEN   A   MAGNET    is    BROKEN    UNLIKE 
APPEAR  AT  THE-  BROKEN  ENDS 


POLES 


A  SERIES  OF  MAGNETS  ACT  AS  ONE 
MAGNET 


24o  GENERAL  SCIENCE 

several  magnets  with  opposite  poles  together,  suggest 
that  the  molecules  of  which  the  iron  is  composed  are 
small  magnets.  When  all  the  molecules  of  a  steel  bar 

are  so  arranged  that 
the  N  pole  of  one 
molecule  is  in  contact 
with  the  S  pole  of  the 

ARRANGEMENT  OP  MOLECULES  IN  next  molecule,  and  SO 

UNMAGNETIZED  IRON  OR  STEEL  on  through  the  entire 

bar  of  steel,  then  all 

the  molecules  at  one  end  of  the  bar  would  have  their  N 
poles  exposed  and  the  molecules  at  the  other  end  would 
have  their  S  poles  exposed.  By  jarring  or  heating  a 
magnet  the  molecules  are  so  disturbed  that  their  align- 
ment is  broken  and  they  arrange  themselves  in  groups 
and  short  chains  until  no  magnetism  is  left.  When  a 
steel  bar  is  being  magnetized,  the  molecules  are  being 
drawn  into  alignment  so  that  opposite  poles  of  the  mole- 
cules touch  one  another.  If  a  steel  bar  is  being  mag- 
netized, jarring  it  while  between  two  poles  of  a  magnet 
will  assist  in  causing  the  molecules  to  take  the  proper 
arrangement.  Soft  iron  is  easily  magnetized,  but  it 
does  not  retain  the  magnetism  like  a  steel  bar. 

165.  Induced  Mag- 
netism. -  -  If  a  tack 
or  a  small  nail  is  sus- 
pended from  the  end 

Of    a    bar    magnet,    a  ARRANGEMENT  OP  MOLECULES^ 

second     tack     can     be  MAGNETIZED  IRON  OR  STEEL 

hung  to  the  first  and 

a  third  to  the  second,  because  each  tack  acts  as  a  magnet 
and  holds  the  one  next  below  it.  If  the  upper  tack  is 
carefully  removed  from  the  bar  magnet,  all  the  other 


MAGNETS 


241 


N 


INDUCED  MAGNETISM  WITH  AND 
WITHOUT  CONTACT 


tacks  will  drop  from  the  first  one,  since  they  do  not 
retain  the  magnetism,  and  act  as  magnets  only  while  in 
the  presence  of  the  bar  magnet  from  which  they  ob- 
tained their  force.  Any  piece 
of  soft  iron  may  be  thus  mag- 
netized temporarily  by  holding 
it  in  contact  with  a  permanent 
magnet;  but  actual  contact  is 
not  even  necessary.  Present 
some  iron  filings  to  one  end  of  a  soft  iron  nail  while  a 
magnet  is  held  near  the  other  end  of  the  nail.  It  will 
be  found  that  the  nail  will  act  as  a  magnet  and  hold 
some  of  the  filings.  Now  lay  a  piece  of  glass  on  some 
filings  or  tacks  and  touch  the  glass  with  the  end  of  a 
good  bar  magnet,  then  lift  the  magnet  and  glass  and  see 
how  many  tacks  are  held  to  the  glass  by  the  magnet. 
Remove  the  magnet  from  the  glass  and  the  tacks  will 
drop.  Several  sheets  of  paper  may  be  used  in  place  of 
glass  and  the  result  will  be  the  same.  Magnetism  pro- 
duced by  such  methods,  with  or  without  contact,  is  called 
induced  magnetism. 

When  a  nail  is  near  a  magnet,  it  becomes  a  magnet  by 
induction.     If  the  N  pole  of  a  magnet  is  placed  near  a 

nail,  the  end  of  the  nail  near 
the  magnet  becomes  an  5  pole 
and  the  other  end  of  the  nail 
becomes  an  N  pole.  The  mag- 
net will  then  pick  up  the  nail, 
because  two  unlike  poles  attract 
each  other.  (See  the  law  of 

magnets.)  The  particles  of  iron  filings  become  magnets 
by  induction  also  when  in  the  field  of  a  magnet.  The  N 
pole  of  one  particle  attracts  the  S  pole  of  the  particle 


SUCCESSIVE  MAGNETIC 
INDUCTION 


242 


GENERAL   SCIENCE 


next  to  the  first  and  so  on  out  from  the  magnet  until  a 
whole  string  of  iron  filings  is  formed.  Since  like  poles 
repel  one  another,  the  outer  ends  of  these  strings  of  iron 
filings  will  have  a  brushlike  appearance;  the  ends  of 
the  strings  being  all  of  the  same  pole  shove  one  another 
apart. 

166.    Magnetic   Field   about   a   Magnet. --The   space 
around  a  magnet  which  is  affected  by  its  force  is  called 

the  magnetic  field  of  the 
magnet.  This  field  is  most 
intense  near  the  poles  of 
the  magnet  and  decreases  in 
strength  as  it  recedes  from 
the  poles.  At  every  point  in 
a  magnetic  field  the  force 

has  a  particular  strength  and  acts  in  a  certain  direction. 
If  a  very  small  compass  is  placed  on  the  side  of  a  bar 
magnet  near  the  N  pole  and  then  moved  in  the  direc- 
tion in  which  the  needle  of  the  compass  points,  it 
will  be  found  that  the  compass  will  take  a  curved  path 


THE  COMPASS  FOLLOWS  THE 
LINES  OF  FORCE  OF  A  MAGNET 


FIELD  ABOUT  A  MAGNET 


toward  the  S  pole  of  the  magnet.     In  this  way  the  whole 
magnetic  field  may  be  mapped  out.     Each  of  the  lines 


MAGNETS 


243 


IRON  FILINGS  SHOW  THE 
FIELD  ABOUT  A  MAGNET 


thus  mapped  out  is  called  a  line  of  force.     These  lines  of 

force  about  a  good  magnet  are  very  numerous. 
A  convenient  way  of  study-  ^^^^^f 

ing  the  field  around  a  magnet 

is  to  place  the  magnet  under  a 

piece  of  paper  covered  with  iron 

filings.      The    filings    will    form 

curves    joining    the   N    and    S 

poles    of    a    bar    magnet,    and 

some    lines    will    go    out    from 

each  pole  which  do  not  seem  to 

join  one  another.     If  a  horse- 
shoe magnet   is   used,   we    find 

lines  of  force  going  straight  across  from  the  N  pole  to  the 

S  pole  and  also  lines  going  in  the  opposite  direction. 

If  opposite  poles,  N 
and  S,  of  two  bar  mag- 
nets are  placed  near  each 
other  under  a  piece  of 
paper  on  which  iron  fil- 
ings are  sprinkled,  it  will 
be  found  that  lines  of 
force  join  the  two  mag- 
nets much  the  same  as 
the  lines  joined  the  two 
poles  of  the  same  mag- 
net. Now  reverse  one 
of  the  two  magnets  so 
that  an  N  pole  is  near 
an  N  pole,  and  sprinkle 
iron  filings  over  the 
paper  again.  Observe 
that  lines  of  force  do  not 


FIELD  ABOUT  N  AND  S  POLES  OF  Two 

MAGNETS,  SHOWING  LINES  OF 

ATTRACTION 


244 


GENERAL  SCIENCE 


pass  from  one  pole  to  the  other,  but  that  the  iron  filings 
are  forced  apart.    Does  this  agree  with  the  law  of  magnets? 

167.  Care  of  Magnets. 
—  If  four  bar  magnets  are 
laid  in  the  form  of  a 
square  so  that  opposite 
poles,  N  and  S,  are  touch- 
ing, a  complete  circuit  for 
the  lines  of  force  will  be 
formed  by  the  magnets  and 
there  will  be  no  external 
magnetic  effect.  (This  can 
be  proved  by  touching 
them  at  various  places 
with  a  nail  or  by  use  of 
iron  filings.)  This  shows 
that  the  steel  of  magnets 
conducts  magnetic  lines 
of  force  better  than  air. 
For  this  reason,  magnets 
while  not  in  use  should 
have  their  opposite  poles  connected  by  an  iron  conductor, 
called  an  armature.  This  iron  becomes  a 
magnet  by  induction  and  the  magnetic 
lines  of  force  pass  through 
it.  Magnets  should  not 
be  jarred  or  heated  as  both 
tend  to  remove  the  align- 
ment of  the  molecules  and 
thus  destroy  their  mag- 
netism. Like  poles  of  two 
good  magnets  should  not 
be  placed  very  near  each 


\\\ 

\S\\V\I 


f 


SHOWING  LINES  OF  REPULSION  OF  Two 
LIKE  POLES  OF  MAGNETS 


How  TO  KEEP  A 
HORSESHOE  MAG- 
NET 


How  TO  KEEP 
Two  BAR  MAG- 
NETS 


MAGNETS  245 

other,  and  especially  not  in  contact,  because  the  stronger 
of  the  two  will  weaken,  reverse,  or  completely  destroy 
the  magnetism  of  the  other,  or  else  make  secondary  poles. 

168.  How  to  Magnetize  Steel.  —  The  simplest  method 
of  magnetizing  a  small  piece  of  steel  is  to  draw  the  steel 
slowly  across  one  end  of  a  magnet.     The  end  of  the  steel 
leaving  the  magnet  will  have  a  pole  opposite  that  of  the 
end   of   the   magnet  across   which 

the  steel  was  drawn.     The  second 

method  is  to  lay  the  steel  on  the     sT  N 

table  and  take  a  bar  magnet  in  each     MAGNETIZING  A  PIECE  OF 

hand  and  touch  opposite  poles,  N 

and  S,  together  on  the  middle  of  the  piece  of  steel  and 

then  slowly  draw  the  magnets  apart  toward  the  ends  of 

the  piece  of  steel. 

169.  The  Earth  a  Magnet.  —  We  have  learned  that  mag- 
nets attract  each  other  if  unlike  poles  are  placed  near  to- 
gether, and  repel  each  other  if  like  poles  are  placed  near 
together,  and  that  magnets  do  not  attract  or  repel  objects 
which  are  not  magnets  or  which  cannot  be  made  magnets 
by  induction,  that  is,  magnets  do  not  attract  or  repel  glass, 
paper,  and  similar  substances.     Hence  we  may  say  that 
magnets  only  attract  or  repel  poles  of  magnets  or  poles 
of  substances  which  are  made  temporary  magnets  by  in- 
duction.    This  being  true,  there  must  be  a  magnetic  pole 
somewhere  in  the   north  which   attracts  one  pole  of  a 
balanced  magnet,  such  as  a  .compass  needle,  and  repels 
the  other  pole,  which  in  turn  is  attracted  by  a  magnetic 
pole  somewhere  near  the  south  geographic  pole. 

We  have  also  found  that  the  needle  of  a  small  compass 
places  itself  parallel  with  the  lines  of  force  coming  from 
the  N  pole  and  going  to  the  S  pole  of  a  bar  magnet. 
Since  a  compass  acts  on  the  earth  the  same  as  it  does 


246 


GENERAL  SCIENCE 


when  in  the  field  of  a  magnet,  the  earth  itself  must  be 
a  magnet  with  an  N  pole  and  an  S  pole.  Since  the  lines 
of  force  passing  from  one  magnetic  pole  of  the  earth  to 
the  other  are  so  weak,  their  effect  on  the  compass  is 
easily  overcome  by  the  strong  field  around  a  bar  magnet. 


MAGNETIC  MERIDIANS 
Showing  lines  of  equal  declination. 

And  yet  the  earth's  lines  of  force  are  strong  enough  to 
move  the  needle  of  the  compass  in  a  north  and  south 
direction  when  no  other  magnet  is  near. 

The  magnetic  poles  of  the  earth  are  not  exactly  at  the 
geographical  north  and  south  poles.  The  magnetic  north 
pole  of  the  earth  is  more  than  1000  miles  away  from  the 
actual  pole,  being  in  latitude  70°  5'  north,  and  longitude 
96°  46'  west.  It  was  located  in  1831  by  Mr.  Ross.  It  is 
just  within  the  Arctic  Circle  in  Boothia  Felix.  The  south 
magnetic  pole  of  the  earth  has  never  been  located.  Be- 
cause of  the  irregularities  in  the  distribution  of  the  magnet- 
ism, there  seem  to  be  two  south  magnetic  polar  regions. 


MAGNETS  247 

Since  the  magnetic  north  pole  is  not  at  the  actual  north 
pole,  a  compass  does  not  point  directly  north  in  the 
United  States  except  on  one  line.  This  line  comes  south 
from  the  magnetic  pole  and  passes  through  central  Ohio 
and  thence  turns  slightly  toward  the  southeast.  A 
compass  anywhere  on  this  line  points  due  north,  but  a 
compass  east  of  the  line  points  west  of  true  north,  and 
one  west  of  the  line  points  east  of  true  north.  At  New 
York  the  compass  points  about  9  degrees  west  of  true 
north,  at  Pittsburgh  about  3  degrees  west  of  true  north, 
and  at  San  Francisco  about  i6f  degrees  east  of  true 
north.  This  variation  of  the  compass  is  called  decli- 
nation. The  declination  of  the  compass  gave  Columbus 
trouble  when  he  crossed  the  Atlantic  the  first  time. 
Mariners  now  have  charts  showing  the  declination  for 
all  parts  of  the  earth.  The  declination  of  the  compass 
at  any  one  place  changes  slightly  from  one  season  to 
another,  but  it  makes  greater  changes  during  a  period  of 
years.  From  1580  to  1816  the  declination  at  London 
changed  from  11°  if  east  to  24°  30'  west,  making  a 
total  change-  of  35°  47'  during  a  period  of  236  years. 

QUESTIONS    AND    EXERCISES 

1.  What  is  the  history  of  lodestone? 

2.  How  can  you  magnetize  your  knife  blade? 

3.  Why  does  a  suspended  magnet  point  north? 

4.  Does  a  magnet  point  due  north  where  you  are?     Why? 

5.  Test  the  law  of  magnets  by  having  one  magnet  suspended 
•and  bring  near  its  poles  the  poles  of  another  magnet. 

6.  How  does  a  magnet  pick  up  a  tack? 

7.  With  a  small  compass  trace  some  lines  of  force  about  a 
bar  magnet. 

8.  How  do  you  care  for  your  magnets?     Why? 

9.  If  the   earth  were  not  a  magnet,  would  a  compass  be  of 
any  value  in  determining  directions?     Why? 


CHAPTER  XXVI 
SIMPLE  ELECTRICAL  APPLIANCES  AND   MACHINES 

170.  Electricity  is  the  name  given  to  an  invisible  agent 
known  to  us  only  by  the  effects  which  it  produces  and  by 
various    manifestations    called    electrical.     These    mani- 
festations, a  few  centuries  ago,  were  obscure  and  even 
mysterious,  but  they  are  now  comparatively  well  known 
to  the  majority  of  people.     However,  the  exact  nature  of 
electricity  is  not  yet  sufficiently  understood  even  by  the 
greatest  scientists. 

171.  Electrification  by  Friction.  —  If  a  piece  of  hard 
rubber  or  a  stick  of  sealing  wax  is  rubbed  with  flannel 
or  cat's  fur  and  then  brought  near  some  dry  bits  of  paper 

or  pith  balls,   these  light  bodies  will 
jump  toward  the  rod.      As  early  as 
600  B.C.   the   Greeks  discovered  that 
rubbed  amber  had  such   characteris- 
tics.     Dr.  William  Gelbert,  the  father 
ELECTRIFICATION    BY     of   modern  science,  in  A.D.   1600  was 
FRICTION  ,       r  ,.  ^1^1 

the  first  to  discover  that  these  same 

The  bits  of  paper        .          .      .      -.  ,  ,  ,  ,          ,  , 

jump  to  and  from  the     electrical  effects  could  be  produced  by 
glass  rod  which  has  a     rubbing   together   a  great  variety  of 

positive  charge.  ? 

other  substances  besides  amber  and 
silk;  such,  for  example,  as  glass  and  silk,  sealing  wax 
and  flannel,  hard  rubber  and  cat's  fur,  or  even  by  rub- 
bing the  hand  on  sheets  of  paper. 

The  electrical  charges  produced  on  these  objects  by 
friction  have  a  peculiar  relation  much  like  the  north- 


ELECTRICAL   APPLIANCES   AND    MACHINES      249 

seeking  and  south-seeking  poles  of  magnets  where  like 
poles  repel  and  unlike  poles  attract  each  other.  The 
electrifications  which  are  imparted  to  glass  by  rub- 
bing it  with  silk  and  to  sealing  wax  by  rubbing  it  with 
flannel  are  opposite  in  the  sense  that  an  electrified  body 
that  is  attracted  by  one  is  repelled  by  the  other.  We 
have,  therefore,  two  kinds  of  electrification,  and  for 
convenience  we  call  one  positive  and  the  other  negative. 
Positive  electricity  is  like  that  on  glass  when  rubbed  with 
silk,  and  negative  electricity  like  that  on  the  sealing  wax 
when  rubbed  with  flannel.  We  also  have  a  law  much 
like  that  applied  to  magnets,  namely,  electrical  charges 
of  like  kind  repel  each  other,  while  electrical  charges  of 
unlike  kind  attract  each  other. 

172.  Lightning  Rods.  —  Benjamin  Franklin  was  the 
first  to  prove  that  lightning  and  electricity  are  the  same. 
During  a  thunder  storm  he  sent  up  a  kite  which  had  a 
sharp-pointed  wire  on  the  top  to  receive  or  discharge 
electricity.  He  used  a  hempen  string  which  became  a 
conductor  after  it  was  wet.  He  held  it  with  a  silk  hand- 
kerchief, a  non-conductor,  so  that  he  would  not  receive 
a  shock.  From  the  metal  key  which  was  tied  to  the 
hempen  string  near  him,  he  was  able  to  draw  electric 
sparks.  This  suggested  to  him  that  the  electric  charge 
in  the  cloud  could  be  neutralized  by  setting  up  a  number 
of  sharp-pointed  rods  which  would  permit  the  induced 
charge  on  the  earth  to  escape  into  the  air.  The  charged 
particles  of  air  would  be  drawn  to  the  charge  in  the  cloud 
since  they  were  of  the  opposite  sign. 

Lightning  rods  made  of  good  conducting  material, 
placed  deep  enough  in  the  ground  to  reach  damp  earth 
(for  dry  earth  is  a  poor  conductor),  and  provided  with 
good  steel  points  on  the  top  of  the  building,  will  neutralize 


250  GENERAL  SCIENCE 

the  heavy  charge  in  an  approaching  cloud  by  sending 
off  a  continuous  stream  of  charged  particles  of  air.  If  a 
lightning  rod  is  not  a  good  conductor  the  induced  charge 
on  the  building  may  become  so  great  that  it  attracts 
the  charge  in  the  cloud.  The  spark  coming  from  the 
cloud,  being  very  large,  will  then  suddenly  rush  to  the 
ground  over  the  lightning  rod  and  may  melt  the  rod  and 
set  fire  to  the  building. 

There  is  no  need  of  being  afraid  during  an  electric 
storm.  It  is  no  safer  in  a  closet  or  a  darkened  room 
than  it  is  in  daylight  or  in  a  well-lighted  room. 
Usually  the  safest  place  during  a  thunder  shower  is 
near  the  middle  of  a  room.  To  get  under  a  tree  stand- 
ing in  an  open  field  is  of  course  dangerous,  because  the 
tree  is  the  only  tall  object  around.  If  a  flash  comes  in 
that  direction  the  tree  will  be  apt  to  conduct  it  to  the 
ground.  It  is  not  so  dangerous  to  stand  under  trees  in 
the  woods  where  there  are  many  trees  as  it  is  to  stand 
under  one  tree  in  an  open  field  during  a  thunder 
shower. 

173.  Current  Electricity.  --To  understand  what  makes 
the  electric  current  flow,  let  us  use  what  we  learned  about 
temperature  and  the  flow  of  liquids.  Heat  will  flow 
from  an  object  with  a  high  temperature  to  an  object  of 
low  temperature  regardless  of  the  quantity  of  heat  in 
either.  If  two  objects  of  different  temperature  are 
placed  together,  the  cooler  one  will  receive  heat  from  the 
warmer  one.  In  the  case  of  liquids,  water  will  flow  from 
a  high  vessel  into  a  low  one  if  they  are  connected  by  a 
tube,  even  though  the  low  vessel  may  have  ten  times  as 
much  water  in  it  as  the  higher  one.  The  water  in  the 
high  vessel  has  a  greater  downward  pressure  than  the 
water  in  the  low  vessel,  hence  the  flow  is  in  the  direction 


ELECTRICAL   APPLIANCES    AND    MACHINES      251 

of  the  greatest  pressure,  or  the  difference  in  pressure  is 
the  cause  of  the  flow. 

The  electric  current  is  caused  by  the  difference  in 
electrical  pressure  at  the  two  ends  of  a  conductor.  This 
difference  of  electrical  pressure  is  called  potential.  (Po- 
tential means  to  be  able,  or  to  have  power.)  Electricity 
flows  from  high  potential  to  low  potential.  High  poten- 
tial is  positive  and  low  potential  is  negative,  so  another 
way  to  designate  the  direction  of  flow  of  electricity  is 
from  positive  to  negative.  These,  however,  are  terms 
used  for  convenience,  as  nothing  definite  is  known  about 
which  way  electricity  flows. 

174.  Electrical  Units.  —  The  difference  in  potential 
at  any  two  points  on  a  conductor  is  the  pressure  that 
makes  the  current  flow  from  one  point  to  the  other. 
All  conductors  offer  some  resistance,  and  hence  this 
pressure  is  necessary.  This  pressure  is  also  called  elec- 
tromotive force  (E.  M.  F.).  The  unit  of  electromotive 
force  is  the  volt,  named  after  Volta,  an  Italian  scientist. 
Electric  lamps  in  the  house  are  usually  lighted  with  a 
current  of  no  volts.  Electric  street  cars  use  from  500 
to  600  volts. 

The  strength  of  current  is  measured  by  a  unit  called  an 
ampere,  named  after  a  French  physicist.  A  unit  current 
is  a  current  of  one  ampere. 

All  conductors  offer  resistance  to  an  electric  current, 
and  the  unit  for  measuring  this  resistance  is  the  ohm. 
We  may  now  define  volt  as  that  potential  difference  or 
E.  M.  F.  which  will  drive  a  current  of  one  ampere  through 
a  resistance  of  one  ohm.  These  units  will  be  more 
clearly  understood  when  we  work  with  electric  cells  and 
machines.  However,  the  relation  that  these  three  units 
bear  to  one  another  can  be  partially  understood  from  the 


252  GENERAL  SCIENCE 

following   expressions   by   which   any   one   of   the   three 
units  can  be  found  if  the  other  two  are  given. 

Electromotive  Force  E 

(1)  Current  =  -    -  -»  or  C  =  -• 

Resistance  R 

Volts 

(2)  Amperes  =  — 

Ohms 

175.  The  Simple  Electric  Cell.  —  Place  some  water 
in  a  small  glass  beaker  or  tumbler  and  then  add  a  few 
drops  of  sulphuric  acid  or  hydrochloric  acid.  Place  in 
it  on  opposite  sides  a  clean  strip  of  zinc  and  one 
of  copper,  as  shown  in  the  figure.  This  is  the  simple 
Voltaic  cell  and  is  capable  of  supplying  a  continuous 
flow  of  electricity  through  a  wire  which  joins  the  strips 
of  copper  and  zinc.  It  will  be  observed  that  the  zinc 
strip  wastes  away  when  the  current  flows.  The  eat- 
ing away  of  the  zinc  by  the  acid  fur- 
nishes the  energy  necessary  to  drive  the 
electric  current  through  the  liquid  of  the 
cell  and  the  external  wire  connection. 
This  cell  may  be  thought  of  as  a 

rr       o/-\  IB  l':_^— ;        fir// 

kind    of    chemical    furnace    in    which 
fuel  is  consumed  to  drive  the  current. 
A  SIMPLE  CELL       Since  zinc  will  burn  in  a  stove,  it  can 
Made   of    copper    be  thought  of  as  the  fuel,  the  acid  is 
the  oxidizer,  and  the  copper  is  a  me- 
tallic  hand  in  the  cell,  which  gathers 
the  current  but  takes  no  part  in  the  chemical  action. 
Before  the  zinc  and    copper  are  connected   by  a  wire, 
the  zinc  is  trying  to  dissolve  in  the  acid  and  throw  a 
current  across  to  the  copper,  while  the  copper  is  also 
trying  to  dissolve,  but  with  less  force,  and- to  throw  a 
current  across  to  the  zinc. 


ELECTRICAL   APPLIANCES   AND    MACHINES      253 

The  potential  or  electrical  pressure  of  the  zinc  is  about 
1.86  volts  higher  than  that  of  the  liquid,  while  the  copper 
has  a  potential  of  only  0.81  volts  higher  than  the  sur- 
rounding liquid,  because  the  copper  is  oxidized  less  easily 
than  the  zinc.  So  the  zinc  has  a  potential  of  about  1.05 
volts  higher  than  the  copper,  but  still  there  will  be  no 
flow  of  electricity  that  can  be  detected  until  the  copper 
is  connected  to  the  zinc  by  a  conductor.  If  the  zinc  and 
copper  are  made  to  touch  at  the  top  or  are  connected  by 
a  long  conductor,  there  will  be  a  rush  of  electricity  through 
the  acid  from  the  zinc  to  the  copper  and  from  the  copper 
to  the  zinc  through  the  external  conductor,  as  indicated 
by  the  arrows  in  the  illustration.  A  small  portion  of  the 
zinc  is  at  the  same  time  dissolved,  the  zinc  parting  with 
its  stored  energy  as  its  atoms  combine  with  the  acid. 
This  energy  is  spent  in  forcing  electricity  through  the 
acid  to  the  copper  strip  and  thence  through  the  external 
circuit  back  to  the  zinc  strip. 

Electricity  flows  from  high  potential  to  lower  potential, 
or  from  positive  to  negative,  represented  by  plus  (+) 
and  minus  (  — )  respectively.  Since  the  current  flows 
from  the  zinc  to  the  copper  in  the  liquid,  the  zinc  is  the 
positive  plate  and  the  copper  the  negative  plate  when 
the  current  in  the  cell  is  under  consideration.  Since  the 
current  leaves  the  cell  by  way  of  the  copper  strip  and 
flows  through  the  wire  to  the  zinc,  the  copper  is  the 
positive  pole  and  the  zinc  is  the  negative  pole,  when  the 
external  circuit  is  under  consideration. 

If  two  copper  wires  are  united  to  the  tops  of  the  two 
strips,  one  to  the  zinc  and  one  to  the  copper,  though  no 
current  flows  as  long  as  the  two  wires  are  kept  separate, 
the  wire  attached  to  the  copper  will  have  a  positive 
charge  and  the  one  attached  to  the  zinc  will  have  a 


254  GENERAL  SCIENCE 

negative  charge,  because  of  the  tendency  of  the  zinc  to 
oxidize  and  drive  a  current  through  the  cell  to  the  copper. 
This  means  that  the  electricity  will  flow  to  the  end  of 
the  wire  and  then  stop  unless  a  connection  is  made  for  a 
complete  circuit.  The  starting  point  of  the  current  is 
not  in  the  wire  but  at  the  zinc  plate  where  chemical 
action  furnishes  the  energy.  As  each  atom  of  zinc 
unites  with  the  acid  molecules  and  liberates  hydrogen 
an  electric  charge  is  produced,  and  the  sum  of  all  of 
these  little  charges  keeps  up  the  potential  difference  or 
electromotive  force  which  drives  the  current  through 
the  entire  circuit.  The  current  is  made  up  of  the  sum 
of  the  charges  carried  by  the  hydrogen  atoms  to  the 
copper  plate.  These  hydrogen  atoms  soon  collect  on 
the  copper  plate  in  such  quantity  that  hydrogen  bubbles 
are  formed.  As  the  hydrogen  collects  on  the  copper, 
making  it  a  less  negative  plate,  the  current  continues  to 
decrease,  because  the  potential  difference  or  electromotive 
force  is  not  sufficient  to  drive,  it.  The  cell  is  said  to  be 
polarized  when  the  copper  plate  is  covered  with  hydrogen 
bubbles.  The  polarization  of  a  simple  cell  takes  place 
so  rapidly  that  the  current  decreases  to  almost  nothing 
in  a  few  minutes. 

If  hydrogen  bubbles  escape  from  the  zinc  when  it  is 
placed  in  the  cell  alone  or  when  the  external  circuit  is  not 
closed,  it  means  that  local  currents  are  set  up  on  the 
zinc  itself,  due  to  the  impurities  in  the  zinc.  The  impu- 
rity in  the  zinc  may  be  iron  or  some  other  metal  which 
receives  the  electric  charge  from  the  hydrogen  atoms 
and  then  the  hydrogen  is  set  free  and  the  current  flows 
from  the  impurity  in  the  zinc  to  the  pure  zinc,  making 
short  circuits.  This  local  action  can  be  prevented  by 
dipping  the  entire  strip  of  zinc  in  dilute  sulphuric  acid  and 


ELECTRICAL   APPLIANCES   AND    MACHINES      255 

then  spreading  over  it  a  thin  coat  of  mercury.  This  process 
is  called  amalgamation.  The  mercury  unites  with  the  zinc 
and  forms  a  pasty  amalgam.  As  the  acid  takes  the 
zinc  out  of  the  amalgam,  the  mercury  unites  with 
other  zinc  beneath  the  surface  and  so  keeps  the  same 
amount  of  amalgam  on  the  surface.  The  iron  does  not 
dissolve  in  the  mercury  but  floats  to  the  surface  of 
the  amalgam,  from  which  a  few  hydrogen  atoms  will 
remove  it. 

176.  How  to  Prevent  Polarization.  —  An  electric  cell 
which  does  not  give  a  comparatively  constant  current, 
for  a  short  time  at  least,  is  not  of  much  value.  There 
are  three  possible  ways  of  preventing  polarization,  but 
only  two  of  them  are  practical. 

(1)  If   the   hydrogen   bubbles   are   brushed   from   the 
copper  plate,  or  if  the  liquid  of  the  cell  is  stirred  suffi- 
ciently, the  bubbles  will  be  removed  and  escape  to  the 
surface.     This  is  a  purely  mechanical  method  and  very 
inconvenient.     Various    modifications    of     this    method 
have  been  devised  but  without  much  success. 

(2)  Chemical  Means.  —  If  there  is  added  to  the  liquid 
of  the  cell  a  substance  which  will  oxidize  the  hydrogen 
as  fast  as  it  is  liberated  at  the  copper  plate,  the  chemical 
action  on  the  zinc  remains  constant  and  so  the  current 
does  not  decrease.     Some  oxidizing  substances  used  are 
bichromate  of  potash,  nitric  acid,  and  manganese  dioxide. 
The  chemical  means  of  preventing  polarization  is  used 
very    extensively.     Manganese    dioxide    (MnC^)    is    the 
depolarizer  in  the  common  dry  cell. 

(3)  Electrochemical  Means.  —  In  this  method  the  copper 
plate  is  in  a  copper  sulphate  solution  and  so  pure  copper 
atoms  are  deposited  on  the  copper  plate  instead  of  hydro- 
gen.    This   prevents    all   polarization   as    the   deposited 


GENERAL  SCIENCE 


DANIELL'S  CELL 


copper  offers  no  more  resistance  to  the  current  than  does 
the  original  plate. 

177.  The  Daniell  Cell.  —  There  are  several  types  of 
the  Daniell  cell.     The  two  common  forms  are  shown  in 

the  illustrations.  The  nega- 
tive pole  is  zinc,  which  is 
immersed  in  dilute  sulphuric 
acid  or  zinc  sulphate  in  an 
unglazed  earthenware  cup. 
The  positive  pole  is  copper, 
which  is  in  a  copper  sulphate 
solution.  The  solution  is 
kept  the  same  strength  by 
the  copper  sulphate  crystals  dissolving  as  copper  is  taken 
out  of  the  solution  and  deposited  on  the  copper  pole. 

The  chemical  action  which  develops  the  current  in 
this  cell  is  as  follows:  The  acid  acts  on  the  zinc  pole  and 
forms  zinc  sulphate  (ZnSO4)  and  free  hydrogen  is  liber- 
ated. The  hydrogen  atoms  with  their  electrical  charges 
pass  through  the  porous  cup  and  come  in  contact  with 
the  molecules  of  copper  sulphate.  The  hydrogen  dis- 
places the  copper  of  the  copper  sul- 
phate and  forms  sulphuric  acid  (H^SCX). 
The  displaced  copper  atoms  take  the 
electrical  charges  from  the  hydrogen 
atqms  and  carry  these  charges  to  the 
copper  pole,  to  which  the  copper  atoms 
adhere  when  they  give  up  their  elec- 
trical charges.  No  polarization  can  oc- 
cur since  no  gas  is  liberated  at  the  positive  pole.  Such 
a  cell  has  an  electromotive  force  of  about  i.i  volts. 

178.  The  'Gravity  Cell  is  so  called  because  the  heavy 
solution  of  copper  sulphate  stays  at  the  bottom  and  the 


GRAVITY  CELL 


ELECTRICAL   APPLIANCES   AND    MACHINES      257 


Carbon 


MODIFIED  LECLANCHE 
CELL 


zinc  sulphate  remains  on  the  top.  The  zinc  plate  dis- 
solves in  the  zinc  sulphate.  The  zinc  of  the  zinc  sulphate 
replaces  the  copper  of  the  copper  sulphate  where  the 
two  solutions  touch.  The  liberated  copper  atoms  are 
thus  given  electrical  charges  which 
they  carry  to  the  copper  plate  at 
the  bottom  of  the  cell  and  they 
adhere  to  the  plate  when  the  charge 
is  given  up.  The  copper  sulphate 
crystals  in  the  bottom  are  dissolv- 
ing to  keep  up  the  strength  of  the 
solution.  Polarization  cannot  occur 
in  this  cell  as  no  gas  is  liberated. 

This  type  of  cell  is  used  extensively  in  telegraphy,  where 
the  circuit  is  kept  closed  nearly  all  the  time. 

179.  The  Dry  Cell.  —  The  dry  cell  is  a  form  of  the 
Leclanche  cell.  It  is  made  by  taking  a  cylindrical  zinc 
cup,  which  serves  as  the  negative  pole,  and  putting  into 
the  middle  of  the  cup  a  carbon  rod  for  the  positive  pole 
and  then  filling  the  intervening  space  with  a  spongy  or 
paste-like  substance  containing  zinc  oxide,  sal  ammoniac, 
zinc  chloride,  plaster  of  Paris,  and  water. 
Sometimes  powdered  manganese  dioxide  is 
mixed  with  the  paste,  and  the  top  is  sealed 
to  prevent  evaporation.  If  the  cell  is  given 
continuous  use,  it  polarizes  in  a  short  time 
and  then  needs  rest  or  time  for  the  hydrogen 
to  be  oxidized  by  the  manganese  dioxide,  or 
to  escape  through  a  small  hole  left  in  the  top. 
The  dry  cell  is  portable  and  is  used,  very  widely  where 
a  continuous  current  is  not  needed.  It  is  convenient 
for  door  bells  and  is  used  for  producing  the  electric 
spark  which  ignites  the  gas  in  gas  engines.  The  com- 


DRY  CELL 


258 


GENERAL  SCIENCE 


CONNECTED  CELLS 

The  cells  in  the  upper  row 
are  connected  in  parallel;  those 
in  the  lower  row,  in  series. 


mon  dry  cell  in  good  condition  has  an  E.  M.  F.  of  about 
two  volts. 

A  battery  consists  of  a  number  of  cells  connected  in 
series  or  in  parallel.    When  cells  are  in  parallel  the  positive 

poles  are  joined  to  positive 
poles  and  the  negative  poles 
to  negative  poles.  When  cells 
are  in  series  they  have  the 
positive  pole  of  one  connected 
with  the  negative  pole  of  the 
next  and  so  on.  The  E.  M. 
F.  increases  when  cells  are  con- 
nected in  series,  and  the  cur- 
rent increases  when  they  are 
connected  in  parallel. 
180.  Magnetic  Field  about  a  Current.  —  From  the 
chapter  on  magnets  we  found  that  a  magnet  has  a  mag- 
netic field  about  it  and  that  the  lines  of  force  come  from 
the  N  pole  and  pass  through  the  air  to  the  S  pole,  and 
that  a  small  compass,  while  held  in  the  magnetic  field, 
points  in  the  direction  in  which  the  lines  of  force  are 
going.  To  show  this,  connect  two  or  more  electric  cells 
in  parallel  and  have  part  of  the  wire  of  the  external  cir- 
cuit in  a  vertical  position  and  passing  through  a  sheet 
of  paper  as  shown  in  the  illustration.  Sift  some  very 
fine  iron  filings  on  the  paper  and  jar  the  paper  very 
gently  to  cause  the  filings  to  adjust  themselves  to  the 
magnetic  lines  of  force  going  around  the  wire.  It  will  be 
found  that  the  wire  is  in  the  center  of  all  the  circles 
formed.  Now  place  one  or  more  small  compasses  on  the 
paper  near  the  wire  and  determine  which  way  the  lines 
of  force  are  traveling.  The  compass  needle  will  point 
in  the  direction  in  which  the  lines  of  force  go. 


ELECTRICAL   APPLIANCES   AND    MACHINES     259 


MAGNETIC  LINES 

ABOUT  A  WIRE 

CARRYING  A 

CURRENT 


Now  determine  whether  the  current  is  going  up  or 
down  through  the  wire,  by  examining  how  it  is  connected 
with  the  poles  of  the  cells.  If  we  change  the  connection 
to  reverse  the  current  we  shall  find  that 
the  compass  needles  will  also  change  their 
direction.  This  means  that  the  lines  of 
force  have  changed  the  direction  in  which 
they  are  going  around  the  wire.  One  way 
of  finding  which  way  the  lines  of  force 
are  going  about  a  wire  carrying  a  current 
is  by  the  right-hand  rule.  Grasp  the  wire 
in  the  right  hand  with  the  thumb  pointing 
in  the  direction  in  which  the  current  is  go- 
ing; the  fingers  then  encircle  the  wire  in  the  same  direction 
as  the  magnetic  lines  of  force. 

Now  let  the  wire  carrying  the  current  be  bent  into  a 
small  coil  of  one  turn  and  insert  a 
small  compass  when  the  coil  is  held 
in  a  north-and-south  position  and 
observe  the  direction  in  which  the 
needle  points.  If  we  reverse  the  di- 
rection of  the  current  by  changing  the  connections  on 
the  cells,  the  needle  will  also  reverse  its  direction.  In 
both  conditions  the  needle  points  in  the  direction  in 
which  the  magnetic  lines  of  force  are 
passing  through  the  coil.  If  these  lines 
of  force  are  followed  by  moving  the 
compass  in  the  direction  in  which  the 
needle  points,  we  find  that  they  come 
out  of  one  side  of  the  coil,  go  around  the 
wire,  and  go  into  the  other  side  of  the  coil.  The  side 
into  which  the  magnetic  lines  of  force  go  is  called  the 
south  pole  of  the  coil  and  the  side  from  which  they 


K 


THE  RIGHT-HAND 
RULE 


LINES  OF  FORCE 
Around  a  single  coil. 


260 


GENERAL  SCIENCE 


CURRENT  THROUGH 

THE  HELIX 
Affects  the  compass. 


come  out  is  the  north  pole.  This  can  be  proved  by 
holding  the  compass  at  either  side  and  observing  which 
pole  of  the  needle  is  attracted. 

Wind  a  wire  around  a  pencil  like  the  threads  on  a 
_«  screw.     Remove  the  pencil  and  con- 

nect the  ends  of  the  wire  forming 
the  coil,  commonly  called  a  helix, 
with  a  good  electric  cell.  Hold  one 
end  of  the  helix  near  a  suspended 
magnet  or  compass  needle.  (See 
illustration.)  The  helix  will  act  in 
every  respect  like  a  magnet,  with  an  N  pole  at  one  end 
and  an  S  pole  at  the  other.  By  reversing  the  helix  and 
pointing  it  at  the  N  pole  of  a  compass  needle  each  time, 
we  can  easily  find  which  is  the  N  pole  of  the  helix  and 
which  end  is  the  S  pole. 
The  magnetic  lines  of  force 
go  into  the  5  pole  end  of 
the  helix  and  come  out  of 
the  N  pole  end.  If  the 
current  goes  around  the 
helix  in  the  right-hand- 
screw  direction,  the  magnetic  lines  of  force  go  through 
the  helix  in  the  same  direction  that  the  current  goes 
from  one  end  to  the  other.  By  reversing  the  current 
the  lines  of  force  will  also  reverse. 

181.  The  Electromagnet.  —  The 
helix  is  a  form  of  electromagnet. 
By  inserting  in  the  helix  an  iron 
rod  which  will  serve  to  conduct 

the  magnetic  lines  of  force,  the  effect  upon  the  compass 
needle  is  much  more  evident.  The  iron  rod  will  also 
pick  up  iron  filings.  By  doubling  the  number  of  turns 


FIELD  ABOUT  A  HELIX 


HELIX  WITH  CORE 


ELECTRICAL   APPLIANCES   AND    MACHINES      261 


HELIX   OF   MANY  TURNS    OF 
WIRE 


of  the  wire  around  the  iron  rod,  its  magnetic  force  will 
be  doubled.  By  doubling  the  current  the  magnetic  force 
will  also  be  doubled.  The 
strength  of  an  electromagnet  is 
determined  by  the  current  or  the 
number  of  amperes  and  the  num- 
ber of  turns  in  the  coil. 

Electromagnets  are  usually 
made  in  horseshoe  form,  with  a  soft  iron  core  extending 
through  each  coil.  The  iron  cores  are  connected  by  an 
iron  bar  called  an  armature.  The  cores 
and  armature  make  a  metallic  circuit 
for  the  lines  of  magnetic  force  and 
prevent  them  from  passing  through  the 
air,  thus  preserving  the  entire  force  of 
the  magnet.  The  iron  object  lifted 
serves  as  a  second  armature.  The  coils 
are  wound  in  such  a  way  that  the 
current  passes  around  them  in  opposite 
directions,  and  therefore  the  poles  of  each  coil  are  re- 
versed. A  soft  iron  core  is  used  because  the  soft  iron 
is  a  magnet  while  a  current  is  pass- 
ing through  the  coil,  and  it  loses  its 
magnetism  as  soon  as  the  current 
is  broken. 

Electromagnets  are  used  for  load- 
ing and  unloading  iron.  A  large 
magnet  is  fastened  to  a  hoisting  SHOWING  POLES,  LINES 

crane  and  lowered  to  a  pile  of  iron.   OF  FORCE'  *ND   DIR£C- 

TION  OF  CURRENT 
The  current  is  turned  through   the 

coils  of  the  magnet  and  the  iron  adheres  to  it.  The 
crane  lifts  the  magnet  with  the  iron  adhering  to  it  and 
swings  it  to  the  desired  place;  the  current  is  then  cut  off 


HORSESHOE 
ELECTROMAGNET 


262 


GENERAL   SCIENCE 


ELECTRIC  BELL 


and  the  load  of  iron  drops  at  once.  Electromagnets  are 
also  used  in  electric  bells,  in  telegraph  and  telephone 
instruments,  and  in  electric  power  generators. 

182.  The    Common   Electric   Bell.  —  The   dry   cell   is 
usually  used  for  the  operation  of  an  electric  bell,  since  a 

continuous  current  is  not  necessary.     In 
the  illustration,  when  the  push  button, 

B,  is  pressed  the  electric  circuit  is  closed, 
and  a  current  flows  from  the  battery  to 

C,  thence  through  the  coils  of  the  elec- 
tromagnet, over  the   closed    contact  A, 
and  out  again  at  D.     No  sooner  is  this 
current  established  than  the  electromag- 
net E  pulls  over  the  armature  a,  and  in 
so  doing  breaks  the  contact  at  A.     This 
stops  the  current,  and  the  magnet  E  at 

once  loses  its  magnetism.  The  armature  is  then  drawn 
back  against  A  by  the  spring  S.  As  soon  as  the  con- 
tact is  made  at  A  the  current  again  begins  to  flow 
and  the  previous  operation  is  repeated.  The  circuit  is 
thus  automatically  made  and  broken 
at  A,  and  the  hammer  h  is  made  to 
vibrate  very  rapidly,  striking  the  bell 
at  each  vibration,  thus  producing  the  PU*H  BuTT°N  FOR 

ELECTRIC  BELL 

ringing  noise. 

183.  The    Telegraph.  —  The    electric    telegraph    and 
the  telegraphic  code  or  alphabet  were  invented  by  S.  F.  B. 
Morse  in  1832.     The  first  public  exhibition  of  the  instru- 
ment was  made  in    1837    m  New  York   City,   when    a 
message  was   sent  over  a   copper  wire    1700   feet  long. 
The  first  commercial  telegraph  line  was  built  in  1844,  be- 
tween Baltimore  and  Washington,  by  the  aid  of  a  $30,000 
grant  from  Congress.     On  May  24,   1844,  the  inventor 


ELECTRICAL   APPLIANCES    AND    MACHINES      263 

sent  the  famous  message,  "What  hath  God  wrought." 
This  was  the  first  message  sent  over  the  wire  from  Wash- 
ington to  Baltimore.  From  that  time  telegraph  systems 
increased  rapidly,  until  now  a  message  can  be  sent  around 
the  world  in  a  few  minutes. 

When  the  key,  K  (see  illustration),  in  Pittsburgh  is 
closed  the  current  flows  over  the  line  to  Chicago.  There 
it  passes  through  the  electromagnet,  M,  and  thence  back 
to  Pittsburgh  through  the  ground.  The  armature,  A, 


SHOWING  THE  PRINCIPLE  OF  THE  TELEGRAPH 

is  held  down  by  the  magnet,  M,  as  long  as  the  key,  K, 
is  kept  closed.  As  soon  as  the  current  is  broken  by 
releasing  the  key,  K,  the  magnet,  M,  is  demagnetized 
and  the  armature,  A,  is  pulled  up  by  the  spring,  S.  By 
means  of  clockwork  the  tape,  T,  is  drawn  along  at  a 
uniform  rate  beneath  the  pencil  or  pen  held  by  the  arma- 
ture, A.  A  very  short  time  of  closing  of  the  key,  K, 
produces  a  dot  upon  the  tape;  if  the  key  is  closed  for  a 
longer  time  a  dash  will  be  produced.  By  this  simple 
method  a  message  could  be  sent  to  Chicago  without  the 
operator  at  Chicago  being  present  at  the  time. 

Many-  improvements  have  been  made  on  the  Morse 
system  so  that  now  operators  can  call  one  another  and 
can  take  a  message  by  sound,  thus  avoiding  the  necessity 
of  having  the  writing  apparatus.  A  very  short  interval 
of  time  between  two  clicks  of  the  sounder  is  interpreted 
as  a  dot,  a  longer  interval  is  interpreted  as  a  dash. 


264 


GENERAL   SCIENCE 


RELAY 


184.   Relay  and  Sounder.  —  On  account  of  the  great 
resistance  in  the  external  circuit  of  long  telegraph  lines, 

it  is  not  possible  to 
drive  a  current  of  suffi- 
cient strength  through 
them  to  operate  the 
electromagnet  of  the 
sounder  so  that  the  ar- 
mature is  drawn  against 
the  post  hard  enough  to  make  a  sound  that  can  be 
heard  distinctly.  Therefore  an  instrument  is  used  which 
is  very  similar  to  the  sounder.  It  is  called  the  relay. 
The  coil  of  the  electro- 
magnet of  the  relay  is 
made  of  many  thousand 
turns  of  very  fine  wire, 
and  the  movable  arma- 
ture is  very  light  in  SENDING  KEY 
order  that  the  feeble 

current  going  through  the  coil  of  the  magnet  can  move  it. 

Since  the  clicks  of  this  light  armature  on  the  relay 

cannot  be  heard,  there  is  at  each  station  a  local  circuit 

with  a  local  battery, 
and  another  instrument 
called  the  sounder,  which 
has  a  heavy  armature 
that  can  be  distinctly 
heard  when  moved  by 
a  strong  electromagnet 
connected  with  the  local 
battery.  The  armature 

on  the  relay  makes  and  breaks  the  local  circuit  so  that 
the  sounder  repeats  the  movements  of  the  relay,  but  with 


Soande 


ELECTRICAL    APPLIANCES    AND    MACHINES      265 

increased  force  because  of  the  local  battery  which  operates 

the  sounder.     The  armature  of  the  sounder  clicks  when 

it  is  drawn  down  by 

the  magnet,  and  also 

when    it    is    drawn 

back  up  by  a  strong  1  ~J-o — J       L 

W  Re/ay  Xe/: 

spring.  The  time 
elapsing  between  two 
successive  clicks  in- 
dicates to  the  oper- 
ator whether  it  is  a 
dot  or  a  dash. 

The  circuit  of  a  telegraph  system  is  kept  closed  when 
not  in  use.  When  the  operator  in  Pittsburgh  wishes  to 
send  a  message  to  Chicago,  he  opens  the  switch  and 


A  TELEGRAPH  SYSTEM 


AMATEUR  WIRELESS  RECEIVING  AND  SENDING  APPARATUS 

operates  the  key  which  makes  and  breaks  the  circuit  as 
the  dots  and  dashes  are  made.     The  sounder  in  Chicago 


266  GENERAL  SCIENCE 

being  in  closed  circuit  responds  to  the  operator  in  Pitts- 
burgh. The  operator  in  Pittsburgh  opens  his  switch 
and  calls  the  operator  in  Chicago  and  then  closes  his 
switch  and  waits  for  a  response.  The  operator  in  Chicago 
opens  his  switch  and  responds  to  the  Pittsburgh  call  and 
then  closes  his  circuit  again.  The  Pittsburgh  operator 
now  opens  his  switch  and  proceeds  to  send  his  message, 
which  the  operator  in  Chicago  writes  as  he  hears  the 
dots  and  dashes. 

185.  Electric  Lights.  —  Most  electric  lights  in  houses 
are  made  to  take  a  current  with  an  E.  M.  F.  of  no  volts. 
The  filament  in  the  lamp  resists  the  flow  of  the  current 
to  such  an  extent  that  it  is  made  white-hot  as  a  result, 
and  thus  radiates  light  and  some  heat.  A  lamp  with  a 
tungsten  filament  takes  about  only  one-third  as  much 
current  as  a  lamp  with  a  carbon  filament,  both  making 
the  same  amount  of  light. 

Since  the  E.  M.  F.  of  the  current  delivered  by  a  60- 
cycle  alternating  generator  is  2200  volts,  it  is  necessary 
to  have  some  way  of  reducing  this 
voltage  so  that  the  lamps  can  use 
it  and  so  it  will  be  safe  to  run  it 
into    the   houses.     A   very   simple 
apparatus,  called  a  transformer,  is 
used  for  the  reduction  of  voltage. 
The    transformer   consists    of    a 
laminated  iron  ring  with  two  coils 
wrapped  on   it.     These   two    coils 
A  xHI^MER          are    not  connected,    and    when    a 
current  passes  through  one  coil  an 
induced  current  passes  through  the  other  coil. 

A  transformer  will  work  only  when  there  is  an  alternat- 
ing current,  because  it  does  not  rotate  through  a  mag- 


ELECTRICAL   APPLIANCES   AND    MACHINES      267 

netic  field.  When  the  lines  of  force  set  up  by  the  primary 
coil  pass  around  the  transformer  and  into  the  secondary 
coil,  a  current  is  induced  which  flows  in  the  opposite 
direction  from  that  in  the  primary  coil.  When  the 
current  in  the  primary  coil  changes  its  direction,  the  lines 
of  force  pass  around  the  transformer  in  the  opposite 
direction  from  that  at  first  and  into  the  secondary  coil, 


ELECTRIC  POWER  PLANT 

and  so  a  current  is  set  up  opposite  to  the  first  current  in 
the  secondary  coil. 

The  voltages  of  the  primary  and  secondary  coils  have 
the  same  ratio  as  the  number  of  turns  of  wire  in  the  pri- 
mary and  secondary  coils.  If  the  voltage  in  the  primary 
is  2  200  and  the  number  of  turns  of  the  primary  on  the 
transformer  is  4400,  the  voltage  in  the  secondary  will 
be  no  if  the  turns  of  the  secondary  on  the  transformer 
are  220.  Transformers  are  usually  enclosed  in  metal 
cases  which  can  be  seen  on  poles  carrying  electric  light 
wires. 


268 


GENERAL   SCIENCE 


186.   The  Telephone. -- The   telephone  was  invented 
by   Alexander    Graham   Bell,    of   Washington,   in    1875. 

It  has  been  in  extensive 
commercial  use  only 
about  25  years.  It  was 
at  first  a  luxury,  but  has 
become  a  necessity  in 
modern  business.  Tele- 
phone lines  are  found 
along  nearly  every  public 
highway.  The  telephone, 
however,  does  not  trans- 
mit sound.  The  sound 
waves  that  are  made 
when  one  speaks  into 

Scientist  and  inventor,  born  March  3,  the  mouthpiece  of  a  tele- 

1847,  educated  in  Edinburgh  and  London,  phone    control    the    elec- 
invented  the  telephone  1875.     HC  also  . 

invented  the  photophone,  induction  bal-  trie  current  which  passes 

ance,  telephone  probe  for  painless  detec-  Qver   the  telephone  wire 


(C)  Underwood  and  Underwood 

ALEXANDER  GRAHAM  BELL 


tion  of  bullets  in  the  human  body,  and 
assisted  in  the  invention  of  the  grapho- 
phone. 


and  into  the  receiver  at 
the  other  end.  The 
current  going  into  the  receiver  causes  an  elastic  piece  of 
sheet  steel  to  vibrate  with  the  same  speed  and  quality 
as  the  voice  of  the  speaker  which  made  the  elastic  sheet 
steel  in  the  mouthpiece  vibrate.  When  the  sheet  steel  in 
the  receiver  vibrates  it  causes  the  air  between  it  and  the 
ear-drum  to  vibrate  and  thus  the  sound  is  carried  to  the 
ear. 

The  modern  telephone  uses  an  induced  current  that 
passes  over  the  wire,  rather  than  the  current  direct  from 
the  battery.  Hence  a  transformer,  a  form  of  induction 
coil,  is  necessary  to  make  the  induced  current.  The 
coil  on  the  transformer  connected  with  the  battery  is 


ELECTRICAL   APPLIANCES   AND    MACHINES      269 

called  the  primary,  and  the  coil  on  the  transformer  con- 
nected with  the  telephone  line  is  called  the  secondary. 
The  current  from  the  battery  goes  to  the  back  of  the 
diaphragm  in  the  mouthpiece,  from  which  the  current 
passes  through  a  little  chamber  which  is  filled  with 
fine  granular  carbon,  to  the  conductor  of  the  trans- 


Linc.  or 


Ground 


SIMPLE  TELEPHONE  SYSTEM 

mitter,  and  thence  through  the  primary,  P,  of  the  induc- 
tion coil  and  then  back  to  the  battery. 

As  the  diaphragm  vibrates  it  varies  the  pressure  on 
the  many  contact  points  of  the  granular  carbon  through 
which  the  current  flows;  this  causes  considerable  'varia- 
tion in  the  resistance  of  the  local  circuit.  When  the 
diaphragm  moves  toward  the  fine  carbon  a  large  current 
flows  through  it  to  the  coil,  P.  When  the  diaphragm 
moves  back  from  the  carbon  a  much  smaller  current 
flows.  These  changes  of  flow  in  the  primary  coil  produce 
a  change  in  the  magnetism  of  the  soft  iron  core  of  the 
induction  coil,  and  there  is  a  like  change  in  the  induced 
or  secondary  current  coming  from  the  secondary  coil  and 
passing  over  the  line  to  the  receiver  at  the  other  end. 


270 


GENERAL  SCIENCE 


This  induced  current  going  into  the  receiver  causes  the 
diaphragm  in  it  to  vibrate  the  same  as  did  the  diaphragm 
in  the  transmitter. 

The  receiver,  as  shown  in  the  illustration  has  a  perma- 

nent long  U-shaped  mag- 
net with  electromagnetic 
coils  on  each  end  of  the 
magnet.  The  coils  are 
made  of  a  large  number 
of  turns  of  fine  wire  and 
each  has  a  soft  iron  core, 

^  end  of  whkh  js  y 


N 


TELEPHONE  RECEIVER 

E,  the  vibrating  diaphragm  and  BB  the 
electromagnets. 


near  the  diaphragm. 
When  the  current  goes  around  these  coils  in  one  direction 
the  permanent  magnet  is  strengthened  and  the  diaphragm 
is  drawn  back  to  the  magnet.  When  the  induced  current 
is  reversed  and  goes  through  the  coils  in  the  reverse 
direction  the  magnetism  of  the  permanent  magnet  is 
overcome  and  the  diaphragm  moves  out  from  the  poles 
of  the  magnet.  These  changes  in 
the  strength  of  the  magnet  are 
made  as  fast  as  the  diaphragm  of 
the  transmitter  vibrates,  and  so 
the  diaphragm  of  the  receiver  vi- 
brates exactly  the  same  as  that  of 
the  transmitter;  thus  the  same  kind 
of  sound  waves  is  transmitted  to 
the  air  as  were  made  by  the  voice 
of  the  speaker.  The  extension  of  the  mouthpiece  is 
simply  to  reflect  the  sound  waves  to  the  diaphragm. 
The  object  in  the  mouthpiece  full  of  holes  is  to  protect 
the  diaphragm. 


TELEPHONE  TRANSMITTER 


ELECTRICAL   APPLIANCES    AND    MACHINERY    271 

QUESTIONS    AND    EXERCISES 

1.  Comb  your  hair  rapidly  with  a  hard  rubber  comb  and 
then  apply  the  comb  to  some  small  pieces  of  paper  or  pith  balls. 
Explain  what  happens. 

2.  Rub  a  glass  rod  with  a  woolen  cloth  or  cat's  fur  and  apply 
the  glass  rod  to  some  small  pieces  of  paper.     Observe  results. 

3.  Compare    these    results    with    the    results    produced    by 
magnets. 

4.  Why  are  lightning  rods  put  on  tall  chimneys? 

5.  Where  is  the  best  place  to  be  during  a  thunder  storm? 
Why? 

6.  What  causes  electricity  to  flow  over  a  wire? 

7.  How  many  volts  and  amperes  are  used  by  your  electric 
lamps  at  home?     (Volts  X    amperes   =    watts.) 

8.  Examine  a  dry  electric  cell.     Will  it  give  a  continuous 
electric  current  very  long?     Why?     Which  pole  is  negative? 

9.  What  practical  use  is  made  of  dry  and  wet  electrical  cells? 

10.  How  can  you  make  an  electromagnet?     What  practical 
uses  are  made  of  electromagnets? 

11.  Examine  your  electric  bell  and  push  button.     Explain 
how  it  works. 

12.  Does  a  telephone  carry  sound?     Explain. 


CHAPTER  XXVII 
LIGHT 

187.  Diffused  Light.  —  From  our  observations  and 
experiences  with  light  and  shadow  we  know  that  light 
travels  in  straight  lines,  except  when  it  is  reflected  by  an 
object  or  refracted  by  passing  into  or  out  of  a  transparent 
substance  at  an  oblique  angle.  When  light  falls  on  rough 
surfaces  like  those  of  trees,  fences,  roads,  etc.,  it  is  re- 
flected in  all  directions.  If  light  falls  on  smooth  water  or 
on  a  mirror  it  is  not  diffused,  but  all  the  light  is  reflected 
in  such  a  way  that  we  see  an  image  of  the  object  from 
which  the  light  is  coming. 

Our  living  rooms  would  be  very  imperfectly  lighted 
if  it  were  not  for  the  reflection  of  diffused  light  through 
the  windows  by  the  objects  outside  and  if  the  walls  of 
the  rooms  did  not  reflect  the  light.  Reflection  of  light 
prevents  the  shade  of  trees  and  houses  from  being  very 
dark.  On  cloudy  days  the  light  of  the  sun  is  reflected 
from  one  drop  of  water  to  another  in  the  cloud  until  it 
finds  its  way  to  the  earth.  The  thicker  the  cloud  the 
less  light  can  get  through,  and  at  times  the  clouds  are 
so  dense  that  artificial  lights  have  to  be  used  to  enable 
us  to  see.  The  air  is  full  of  very  small  dust  particles. 
The  light  reflected  back  and  forth  from  these  par- 
ticles of  dust  helps  to  give  the  sky  a  blue  color  on  clear 
days.  Fine  water  particles  like  mist  give  the  sky  a  gray- 
ish color, 


LIGHT 


273 


188.  Lenses.  —  Converging  lenses  are  thick  in  the 
center  and  thin  at  the  edge.  The  light  which  passes 
through  them  is  refracted  or  bent  from  its  straight  path 


LENSES 
a,  b,  and  c,  are  Converging,  and  d,  e,  and/,  Diverging  Lenses. 

so  that  it  will  pass  through  a  point.  These  lenses  are 
used  in  simple  magnifying  glasses,  microscopes,  tele- 
scopes, cameras,  and  in  eye-glasses  for  farsighted  people. 

Diverging  lenses  are  thin  in  the  center  and  thick  at 
the  edge.  The  light  which  passes  through  them  is  made 
to  diverge  or  spread  apart.  They  are  used  in  eye-glasses 
for  people  who  are  nearsighted,  and  sometimes  they  are 
used  in  the  small  end  of  opera  glasses. 

189.  Cameras.  —  With  a  pin  or  pencil  make  a  small 
hole  in  a  sheet  of  paper  and  hold  it  before  a  light  or 
toward  a  win- 
dow; place  back 
of  the  hole  an- 
other sheet  of 
paper,  and  on  it 
you  will  see  a 
picture  or  image 
of  the  object 
from  which  the 

light  is  coming.  This  is  known  as  a  "pin  hole"  camera. 
A  picture  can  be  taken  with  it  if  a  light-tight  box  is 


FORMATION  OF  A  PINHOLE  IMAGE 


274  GENERAL  SCIENCE 

made  and  a  sensitive  plate  is  exposed  in  it  back  of  the 
pin  hole,  which  acts  as  a  lens. 

A  camera  is  a  box,  black  inside,  and  made  so  that 
light  can  enter  only  through  a  converging  lens.  The 
lens,  when  focused,  throws  an  image  on  a  plate  or  film 
which  is  covered  with  a  chemical  that  is  sensitive  to 
light;  each  part  of  the  plate  is  affected  according  to  the 
amount  of  light  striking  it.  The  light  parts  of  an  object 
which  is  being  photographed  throw  more  light  into  the 
camera  than  the  darker  parts,  and  these  light  parts  of 
the  object  will  affect  the  sensitive  plate  more  than  the 
darker  parts.  The  exposed  plate  is  developed  by  washing 
it  in  the  proper  chemicals,  and  it  is  then  known  as  the 
"negative,"  because  its  shades  are  opposite  to  those  of 
the  object  photographed.  Positive  prints  are  made  by 
allowing  light  to  pass  through  the  negative  to  sensitive 
paper,  which  is  then  developed  by  washing  it  in  the 
proper  chemicals. 

190.  The  Spectrum.  —  When  a  beam  of  ordinary  white 
light  passes  through  a  prism  it  is  not  only  refracted  but  is 

also  dispersed,  i.e.  it  is 
separated  into  what  ap- 
pears to  the  eye  as  a 
series  of  different  hues 
or  colors,  called  a  spec- 

SPECTRUM  FORMED  BY  A  GLASS   PRISM    trum'     ^  order  of  the 

colors  in  such  a  spec- 
trum is  red,  orange,  yellow,  green,  blue,  and  violet,  the 
red  having  the  least,  and  the  violet  the  greatest,  angle  of 
deviation,  as  shown  in  the  diagram. 

191.  Rainbow.  —  A  very  beautiful  natural  spectrum, 
with  which  everyone  is  familiar,   is  the  rainbow.     The 
rainbow  is  usually  seen  just  after  a  rain  during  the  latter 


LIGHT 


275 


part  of  the  day,  when  the  bright  sun  appears  before  the 
cloud  has  disappeared.  The  reason  that  a  rainbow  is 
not  seen  in  the  morning  is  because  the  clouds  as  a  rule 
travel  from  west  to  east,  and  the  front  of  the  cloud  usually 
hides  the  sun  before  any  rain  falls.  After  the  cloud  is 
past,  the  sun  is  not  in  the  right  position  to  shine  on  the 
falling  drops.  So  rainbows  are  seen  by  looking  east  just 
after  a  shower,  and  usually  in  summer,  because  the 
winter  clouds  do  not  pass  away  quickly  enough  for  the 
sun  to  shine  on  the  falling  rain. 

To  understand  how  a  rainbow  is  made,  let  us  examine 
the  illustration.    MN  is  a  large  cardboard  with  an  opening 
at  O  for  the  light  of  the  sun  to  enter  the  room.     The 
light  passes  into  the  two- 
inch  spherical  flask  at  A, 
and  is  refracted  as  it  enters, 
just   as  when   light   passes 
through  a  prism.     It  goes 
through   the   water   to   the 
other  side  of  the  flask  at  B, 
from  which  it  is  reflected  to 
C.     As  it  comes  out  of  the 

flask  at  C  it  is  refracted  again,  thus  spreading  the  red 
and  violet  rays  farther  apart.  From  C  the  light  goes  to 
the  cardboard,  with  the  violet  and  red  at  the  positions 
indicated  and  the  other  colors  of  the  spectrum  between 
the  red  and  violet.  Since  violet  is  refracted  most,  it  will 
be  nearest  the  center  of  the  circle.  Only  one  ray  of  light 
is  represented  in  the  drawing,  but  the  rainbow  spectrum 
is  a  complete  circle  around  the  hole  0. 

The  natural  rainbow  seen  after  a  rain  is  due  to  the 
refraction  of  the  sunlight  as  it  passes  into  and  out  of  a 
drop  of  falling  water  and  the  reflection  of  this  light  from 


PRODUCING  AN  ARTIFICIAL  RAINBOW 


2  76  GENERAL  SCIENCE 

the  opposite  surface  of  the  drop  so  that  it  comes  out 
of  the  drop  in  the  direction  toward  us.  The  falling 
drops  act  on  the  light  just  as  the  flask  in  the  illustra- 
tion did. 

The  illustration  on  this  page  represents  a  natural 
rainbow  with  a  secondary  one  above  it.  The  secondary 
bow  is  usually  seen  only  in  part.  Since  the  rainbow  is 
in  a  comparatively  fixed  position  at  any  one  time,  and 
since  a  drop  of  falling  water  must  be  in  a  certain  position 

with  respect  to  us  in 
order  to  refract  and 
reflect  the  light  to 
us,  the  time  during 
which  one  drop  helps 
to  make  the  rainbow 
is  a  very  small  frac- 

SHOWING  HOW  PRIMARY  AND  SECONDARY      tion  of  a  second.      So 
RAINBOWS  ARE  FORMED  ,,      .  ,,.        , 

the  falling  drops  must 

be  quite  numerous  in  order  to  make  a  continuous  colored 
arch.  Since  violet  is  refracted  more  than  red,  the  violet 
appears  on  the  inside  of  the  circle  and  the  red  at  the 
outer  edge,  with  the  other  colors  between.  As  the  drop 
descends  through  the  position  where  it  will  throw  the 
colors  to  our  eye,  the  ray  of  light,  a,  passes  into  the  lower 
part  of  the  drop,  is  reflected  twice  from  the  opposite  sur- 
face, and  then  refracted  again  as  it  comes  out.  As  violet 
is  refracted  most,  the  drop  will  throw  violet  color  to  our 
eyes  first  from  position  v,  followed  by  the  other  colors  of 
the  spectrum,  ending  with  red  in  position  r.  From  r  the 
drop  passes  down  into  a  space  from  which  it  cannot  throw 
any  colors  to  our  eyes  until  it  descends  to  position  /. 
Here  the  ray  of  light  fr,  passing  into  the  upper  part  of 
the  drop,  is  refracted,  then  reflected  from  the  opposite  side, 


LIGHT  277 

and  refracted  again  as  it  leaves  the  drop.  Since  red  is  not 
refracted  so  much  as  violet,  the  drop  throws  first  to  our 
eyes  red  and  then  the  other  colors  of  the  spectrum,  ending 
with  violet  from  the  position  z>'.  As  the  drop  falls  fromY, 
it  does  not  cast  any  color  into  the  eye  at  E. 

The  distance  of  the  falling  drops  from  the  eye  is  what 
determines  the  height  of  the  rainbow.  The  reason  that 
the  rainbow  is  an  arc  of  a  circle  is  because  every  drop 
that  throws  the  colors  to  the  eye  must  be  in  a  certain 
position  with  respect  to  the  eye.  If  a  line  is  drawn  from 
the  eye  to  the  center  of  the  circle  of  which  the  rainbow 
is  a  part,  all  of  the  drops  of  water,  while  passing  through 
the  rainbow  are  equally  distant  from  the  eye  and  any 
point  on  the  line.  This  line  drawn  from  the  eye  to  the 
center  of  the  circle  of  which  the  rainbow  is  an  arc 
forms  an  angle  of  40°  with  the  line  drawn  from  the 
eye  to  the  violet  color  of  the  rainbow,  and  an  angle 
of  42°  with  the  line  drawn  from  the  eye  to  the  red  part 
of  the  rainbow.  If  a  person  were  on  top  of  a  very 
high  building  it  would  be  possible  to  see  almost  the 
complete  circle  of  the  rainbow.  While  standing  on  the 
ground,  where  it  is  level  or  nearly  so,  not  quite  one- 
half  of  the  circle  can  be  seen. 

No  two  persons  can  see  exactly  the  same  rainbow,  be- 
cause the  eyes  must  be  at  a  given  angle  from  the  drops 
that  make  the  colors.  When  a  person  moves,  the  rain- 
bow moves  also.  If  we  move  toward  the  rainbow,  it 
may  keep  at  about  the  same  distance  from  us  as 
when  we  started,  depending  upon  how  fast  the  cloud 
is  moving. 

A  rainbow  spectrum  can  be  made  with  a  street  sprinkler, 
hose,  or  sprayer  in  the  morning  or  afternoon  when  the 
sun  is  shining.  Glass  prisms  on  lamps,  angles  in  glass 


278  GENERAL  SCIENCE 

doors,  cracked  glass,  and  waves  of  water  will  produce 
refraction  of  light  so  that  the  rainbow  colors  can  be  seen. 

QUESTIONS    AND    EXERCISES 

1.  What  kind  of  objects  can  be  seen?     Which  kind  cannot  be 
seen? 

2.  To   have   properly   lighted   rooms,    what   color   of   paper 
should  be  on  the  walls?     Why? 

3.  What  practical  uses  are  made  of  lenses? 

4.  Bring  your  camera  to  school  and  learn  the  use  of  its  parts 
so  you  can  take  better  pictures. 

5.  What  time  of  the  day  are  most  rainbows  seen?     Why? 
What  is  the  arrangement  of  the  colors  of  a  rainbow? 

6.  How  can  rainbow  colors  be  produced  on  a  clear  day? 


CHAPTER  XXVIII 


Ciliary  Muscle 


THE  HUMAN  EYE 

192.  Structure  of  the  Eye.—  The  complete  eye  consists 
of  three  parts,  namely,  the  eyebrows,  which  prevent  per- 
spiration and  dust  from  touching  the  eyeball;  the  eyelids, 
which  protect  the  eyeball  and  keep  out  dust;  and  the 
eyeball  itself.  The  normal  eyeball  is  nearly  spherical  and 
the  outer  part  is  composed 
of  three  layers;  the  inner 
part  is  filled  with  three 
transparent  substances,  two 
of  which  are  almost  like  thin 
jelly  in  texture. 

The  illustration  shows  the 
parts  of  the  eye.  The  front 
part  is  a  very  tough  sub- 
stance called  the  cornea. 
The  cornea  has  the  power 
of  refracting  light  and  acts 
as  a  converging  lens.  Just 
back  of  the  cornea  is  a  watery  liquid  called  aqueous  humor. 
It  is  transparent  and  helps  to  hold  the  cornea  in  position. 
Back  of  this  aqueous  humor  is  a  thin  muscle  called  the 
iris.  The  iris  is  the  middle  layer  of  the  outer  part,  and 
it  goes  all  around  the  eyeball.  The  color  of  the  iris  in 
front  gives  the  various  colors  to  the  eyes,  such  as  gray, 
blue,  or  brown.  The  iris  has  a  round  hole  in  it  which  is 
called  the  pupil  of  the  eye.  The  iris,  a  muscle,  changes 


SECTION  THROUGH  THE  EYE 
Showing  the  parts. 


280  GENERAL  SCIENCE 

the  size  of  the  pupil  to  regulate  the  amount  of  light  enter- 
ing the  eye. 

While  we  are  in  the  sunlight  or  in  a  room  where  the 
lights  are  bright,  the  pupil  is  small,  but  when  we  are  in 
the  dark  the  pupil  is  very  large.  The  changing  of  the 
size  of  the  pupils  of  your  eyes  can  be  seen  by  going  sud- 
denly from  a  dark  room  into  a  lighted  room  and  watching 
for  the  change  by  looking  into  a  mirror;  or  by  closing 
the  eyes  for  a  moment  in  a  lighted  room  and  then  open- 
ing them  suddenly  and  looking  into  a  mirror.  When  we 
go  from  the  bright  sunlight  into  a  house,  especially  if 
snow  is  on  the  ground,  we  cannot  see  distinctly  for  a 
while,  because  the  iris  does  not  adjust  itself  quickly  after 
being  in  strong  light  for  some  time. 

Just  back  of  the  iris  is  the  colorless  crystalline  lens, 
which  is  double  convex  and  refracts  the  light  and  forms 
an  image  just  as  does  the  lens  in  a  magnifying  glass. 
The  crystalline  lens  is  held  in  position  by  a  ligament 
which  goes  entirely  around  it,  much  like  the  frame  of 
a  magnifying  glass  which  holds  the  lens.  The  crystalline 
lens  can  change  its  shape  and  can  become  thicker  or 
thinner  through  the  center.  When  the  ligament  around 
the  lens  is  loosened  by  the  action  of  a  muscle,  the  thick- 
ness of  the  lens  is  increased.  When  this  circular  muscle 
relaxes,  then  the  ligament  in  which  the  lens  is  held  pulls 
outward  and  makes  the  lens  thin  but  broader.  When 
we  read,  the  lens  is  made  thick;  when  we  observe  distant 
objects  the  lens  is  made  thin  or  less  convex,  so  that  the 
image  formed  by  it  falls  on  the  right  place. 

Back  of  the  crystalline  lens  is  the  largest  part  of  the 
eye,  which  is  filled  with  a  transparent  substance  called 
vitreous  humor.  This  helps  to  keep  the  eyeball  in  shape 
and  acts  somewhat  as  a  lens.  The  retina  lines  the  entire 


THE   HUMAN  EYE 


281 


cavity  containing  the  vitreous  humor.  It  contains  the 
nerves  of  sight  and  is  connected  with  the  large  optic 
nerve. 

The  eye  is  a  much  more  perfect  optical  instrument  than 
the  camera.  The  lens  of  the  camera  must  be  moved  back 
and  forth  until  a  distinct  image  is  formed  on  the  screen. 
The  lens  must  also  be  changed  for  various  distances. 
The  eye  adjusts  itself  almost  instantly  to  form  images  of 
near  and  far  objects.  The  image  formed  by  a  normal 
eye  is  much  more  distinct  and  accurate  than  the  image 
formed  by  the  lens  of  a  camera.  The  crystalline  lens, 
instead  of  moving  back  and 
forth  to  accommodate  itself 
to  various  distances,  simply 
changes  its  shape.  For  near 
objects  it  thickens,  thus  in- 
creasing the  curvature  and 
making  the  lens  more  con- 
vex, so  that  it  can  focus  the  close  vision  Distant  vision 
rays  of  light  on  the  retina.  SECTION  OF  THE  FRONT  or  THE  EYE 

Showi 

close  and  distant  vision. 


Ligan 


Muscle 


For  distant  objects  the  crys-     Showing  the  change  of  the  lens  for 


talline  lens  is  made  thin 
and  less  convex,  so  that  the  rays  of  light  are  not  focused 
before  they  get  back  to  the  retina.  This  process  of 
adjustment  of  the  crystalline  lens  is  called  accommodation. 

193.  How  We  See  Objects. —  Nearly  all  objects  re- 
flect light,  and  this  reflected  light  passes  through  the 
cornea  and  is  slightly  refracted.  The  cornea  acts  as  a 
converging  lens.  The  light  then  passes  by  way  of  the 
pupil  through  the  crystalline  lens,  which  is  double  convex 
and  continues  the  refraction  started  by  the  cornea.  An 
image  of  the  object  is  formed  on  the  retina.  The  retina 
contains  nerves  and  is  sensitive  to  this  light  forming  the 


282  GENERAL  SCIENCE 

image.  The  disturbance  in  the  nerve  caused  by  the 
image  is  carried  by  the  optic  nerve  to  the  brain,  where  it 
is  interpreted,  and  then  we  become  conscious  of  the  pres- 
ence of  an  object  in  our  field  of  vision.  We  see  objects 
because  they  reflect  light  into  the  eyes  or  because  the 
objects  are  self-luminous.  Our  eyes,  of  course,  reflect  light 
so  that  another  person  can  see  them,  but  that  part  of  the 
eye  just  in  front  of  the  pupil  does  not  reflect  any  light, 
therefore  the  pupils  of  every  person's  eyes  are  black,  and 
we  can  only  distinguish  the  pupil  of  the  eye  by  means  of 
contrast.  The  iris,  a  muscle  which  regulates  the  size  of 
the  pupil,  having  the  color  blue,  gray,  or  brown,  reflects 
light  as  does  the  white  part  of  the  eyeball. 

The  nerves  of  the  retina  are  able  to  receive  about  ten 
image  impressions  per  second;  that  is,  if  ten  objects  were 
shown  to  us  in  a  second,  we  could  see  each  one  distinctly. 
If  less  than  ten  are  shown,  we  of  course  see  them 
separately  and  each  one  makes  a  distinct  impression. 
If  more  than  ten  objects  are  shown  to  us  in  a  second,  we 
cannot  distinguish  one  from  the  other  and  they  appear  as 
a  continuation  of  one  object.  If  a  stick  with  a  spark  of 
fire  on  the  end  is  whirled  rapidly,  we  see  a  streak  of  fire 
and  not  a  spark  in  distinct  successive  positions.  This  is 
because  the  stick  gets  around  the  circle  and  makes  a 
second  impression  or  image  on  the  retina  before  the  im- 
pression of  the  first  image  is  gone.  The  separate  spokes, 
in  a  rotating  wheel  cannot  be  seen  for  the  same  reason. 
The  wheel  of  a  rapidly  moving  automobile  seems  to  be 
solid  and  not  made  of  spokes.  Moving  pictures  are 
operated  on  the  same  principle.  A  reel  contains  about 
1,000  separate  pictures  an  inch  square.  These  are  made 
to  pass  the  lens  in  the  projection  lantern  at  the  rate  of 
fifteen  or  sixteen  per  second.  Each  picture  shows  the 


THE   HUMAN   EYE 


283 


actors  in  a  very  slightly  different  position  and  so  the 
observer  gets  the  impression  that  the  actors  are  actually 
moving  in  the  picture.  Sometimes  thirty  pictures  are 
thrown  on  the  screen  per  second;  this  gives  a  better 
effect  than  sixteen  per  second. 

194.  Defects  of  the  Eye.  —  There  are  two  common  de- 
fects of  the  eye  caused  by  the  eyeball  not  having  the 
proper  shape  and  by  the  inability  of  the  crystalline  lens 
to  adjust  itself  to  various  dis- 
tances. Such  eyes  lack  normal 
accommodation.  The  remedy  is 
to  wear  glasses  with  lenses  of  the 
proper  shape  to  make  up  for  the 
defect  of  the  eye. 

(a)  Nearsightedness. —  This  is 
most  often  due  to  the  eye  being 
too  long  from  front  to  back.  The 
rays  of  light  are  brought  to  a 
focus  before  reaching  the  retina  Showing  the  defect  in  A  and 

which   makes   the    object  appear    the  correction  with  a  concave 

blurred  or  else  it  is  not  visible  at 

all.  Sometimes  nearsightedness  is  the  result  of  the 
cornea  or  the  crystalline  lens  being  too  convex.  This  is 
usually  caused  by  a  weakening  of  the  eyeball  and  does 


NEARSIGHTED  EYES 


A 

FARSIGHTED  EYES 
Showing  the  defect  in  A  and  the  correction  with  a  convex  lens  in  B. 

not  occur  often  in  very  young  children.     The  remedy  for 
nearsightedness  is  to  wear  glasses  with  diverging  lenses. 


284  GENERAL  SCIENCE 

(b)  Farsightedness  is  caused  by  the  eyeball  being  too 
short  from  the  front  to  the  back  or  by  the  crystalline 
lens  not  being  sufficiently  convex  to  bring  the  light  to 
a  focus  on  the  retina.  The  light  is  not  focused  soon  enough 
to  see  objects  that  are  near.     The  person  thus  affected 
can  often  see  distant  objects  better  than  a  person  with  a 
normal  eye,  and  usually  holds  a  paper  at  arm's  length 
when  he  reads.     Farsightedness  is  a  very  common  defect 
among  people  after  they  pass  the  age  of  fifty  years.     With 
young  people  it  is  rare.     The  remedy  is  to  wear  glasses 
with  converging  lenses. 

(c)  Color  Blindness. —  Men  as  a  rule  are  not  as  much 
interested  in  the  various  shades  of  color  as  are  women, 
and  so  they  are  not  able  to  distinguish  colors  so  readily, 
that  is,  to  call  them  by  name.     This  does  not  mean  that 
men  are  unable  to  distinguish  a  difference  between  two 
shades  of  color,  but  that  they  may  be  unable  to  name  the 
difference  or  even  to  name  the  colors  under  consideration. 
This  is  due  to  a  lack  of  knowledge  on  the  part  of  men  and 
not  to  a  defect  of  the  eye. 

Color  blindness  is  a  defect  of  the  eye  which  makes  it 
unable  to  distinguish  any  difference  between  certain  colors. 
Red  and  green  with  their  various  shades  are  the  colors 
which  color-blind  persons  are  unable  to  recognize.  Their 
eyes  do  not  respond  to  the  ether  waves  that  produce  the 
sensation  of  red  and  green  in  the  normal  eye.  The  cause 
of  the  defect  is  not  known  and  so  cannot  be  remedied. 
Some  investigators  say  that  one  out  of  every  twenty  male 
persons  is  color  blind,  while  only  one  out  of  every  two 
hundred  females  has  the  same  defect.  Red  and  green 
lights  are  the  danger  and  safety  signals  used  by  the  rail- 
roads and  navigation  companies,  therefore  it  is  very 
important  for  engineers  and  pilots  not  to  be  color  blind, 


THE  HUMAN  EYE  285 

Transportation  companies  do  not  put  men  who  are  color 
blind  in  positions  where  safety  is  dependent  upon  recog- 
nizing red  and  green  lights. 

(d)  Astigmatism  and  Headache. —  Astigmatism  is  a  de- 
fect due  to  improper  curvature  of  the  cornea  or  crystalline 
lens  so  that  the  light  is  not  properly  focused,  and  imper- 
fect images  on  the  retina  result.  The  muscles  of  the  eye 
are  continually  trying  to  adjust  the  parts  of  the  eye  to 
form  clear  images.  These  overworked  muscles  soon  be- 
come painful.  The  pain  is  felt  in  and  around  the  eyeball 
and  often  in  the  front  part  of  the  head,  where  it  is  known 
as  headache.  Headache  and  smarting  of  the  eyes  after 
continued  use,  if  the  light  is  properly  adjusted  and  the 
work  not  more  than  the  normal  eye  can  stand,  are  signs 
of  astigmatism. 

Headache  and  pain  in  the  eyes  are  often  caused  by 
improper  use  of  the  eyes,  such  as  reading  or  sewing  in 
glaring. or  dim  lights  or  by  overwork  in  a  place  properly 
lighted.  Reading  ordinary  print  on  a  moving  train  or 
electric  car  soon  produces  pain  in  the  eyes  for  most 
people,  because  of  the  continuous  use  of  the  muscles  in 
keeping  the  parts  adjusted  and  the  eye  directed  to  a  defi- 
nite spot  on  the  shaking  paper. 

The  remedy  for  astigmatism  is  to  wear  glasses  of  the 
proper  kind,  prepared  under  the  direction  of  a  well- trained 
oculist.  The  pain  in  the  eyes  and  headache  caused  by 
astigmatism  will  be  relieved  if  the  proper  shaped  lenses 
are  secured.  Sometimes  astigmatism  may  be  perma- 
nently cured  if  the  eyes  are  properly  treated  and  cared 
for. 

195.  Care  of  the  Eyes. —  Numerous  investigations  have 
shown  that  most  children  are  born  with  good  eyes,  and 
that  the  eyes  become  injured  through  improper  use. 


286  GENERAL  SCIENCE 

Children  after  starting  to  school  often  weaken  their  eyes 
by  studying  where  the  lights  are  too  dim  or  too  bright, 
or  by  sitting  so  that  the  light  can  shine  into  the  eyes,  or  by 
reading  books  containing  too  fine  print. 

A  book  or  paper  should  be  held  from  ten  to  fifteen  inches 
from  the  eyes  for  average  sized  print.  While  reading,  the 
head  should  be  held  almost  erect  and  the  light  so  placed 
that  it  does  not  shine  into  the  eyes;  if  possible  the  light 
should  come  over  the  left  shoulder.  Trying  to  read  in 
dim  light  and  leaning  the  head  forward  while  reading 
cause  pressure  on  the  eyeballs,  and  nearsightedness  may 
result.  The  eyes  need  rest  the  same  as  any  other  part 
of  the  body.  If  the  eyes  pain  after  long-continued  work, 
the  muscles  controlling  their  adjustment  need  rest.  Do 
most  reading,  writing,  and  sewing  in  daylight,  especially 
if  your  eyes  are  slightly  weak.  Use  shades  on  lamps,  be- 
cause most  lamps  throw  most  of  their  light  upward  and 
cast  a  shadow  at  their  base.  This  shadow  often  falls  on 
the  book  being  read  if  a  shade  is  not  used  to  reflect  the 
light  downward.  If  properly  used,  the  shade  will  also 
keep  the  light  from  shining  directly  into  the  eyes.  In- 
flamed or  weak  eyes  are  often  aided  by  bathing  with  a 
cupful  of  lukewarm  water  in  which  a  teaspoonful  of  boracic 
acid  has  been  dissolved. 

196.  Light  and  Health. —  Sunlight  is  essential  to  the 
growth  of  trees,  vegetables,  and  the  cereal  grains.  These 
plants  have  a  pale  green,  sickly  look  when  for  several 
days  they  do  not  get  the  proper  amount  of  light.  The 
heat  and  light  of  the  sun  furnish  directly  the  energy  for 
the  growth  of  plants  upon  which  man  is  dependent  for 
food,  clothing,  and  shelter.  Artificial  light  is  not  sufficient 
for  the  growth  of  vegetation. 

Man,  like  plants,  without  sunlight  turns  pale,  has  a 


THE   HUMAN  EYE  287 

sickly  appearance,  and  his  blood  loses  much  of  its  ability 
to  destroy  the  tiny  one-celled  organisms  which  exist  there 
in  countless  numbers.  By  working  in  the  open  air  and 
sunshine  the  body  is  kept  in  good  physical  condition 
and  is  then  able  to  resist  the  attacks  of  most  foreign 
one-celled  organisms.  Bacteria,  one-celled  organisms,  live 
mostly  in  dark,  damp  places  and  are  not  accustomed  to 
much  light.  When  they  are  exposed  to  sunlight,  they  die. 
For  this  reason  living-rooms  should  be  well  lighted  and 
as  much  of  the  direct  sunlight  should  be  permitted  to 
enter  the  rooms  as  possible.  The  injury  to  the  paper  on 
the  walls  and  to  the  carpet  is  not  so  expensive  as  ill- 
health.  Faded  paper  does  not  produce  the  discomfort 
that  lost  health  does.  Paper  and  carpets  that  do  not 
fade  perceptibly  in  the  presence  of  sunlight  should  be 
selected. 

Hospitals  are  now  built  so  that  most  of  the  rooms 
receive  the  direct  rays  of  the  sun  during  part  of  the  day. 
Patients  are  often  required  to  sit  in  the  sun  and  open 
air.  The  sleeping  quarters  of  tuberculosis  sanatoriums 
are  built  with  three  open  sides  so  that  abundant  light 
and  air  can  enter.  The  recreation  sheds  are  built  with 
the  south  side  entirely  open  so  that  the  sun  can  shine 
into  them.  Sunlight  and  fresh  air  are  the  two  great  pre- 
ventives of  disease,  and  they  will  help  to  cure  many 
diseases. 

Artificial  lights  unfortunately  do  not  kill  many  germs. 
Public  buildings  and  offices  where  artificial  lights  must 
be  used  all  the  time  are  not  the  most  healthful  places 
in  which  to  work.  Such  rooms  and  offices  should  be  fre- 
quently disinfected.  Many  modern  church  buildings  have 
such  dark  colors  in  the  "memorial  and  picturesque" 
windows  that  scarcely  a  ray  of  sunlight  can  ever  enter 


288  GENERAL  SCIENCE 

to  remove  some  of  the  dungeon-like  gloom  and  throw 
a  ray  of  hope  into  the  hearts  of  the  occupants,  as  well  as 
to  remove  some  of  the  disease  germs  that  may  be  lurking 
there  waiting  for  a  victim.  Modern  factory  builders  have 
come  to  recognize  the  valuable  effects  of  light  on  the  work- 
men, and  such  buildings  are  filled  with  numerous  large 
windows.  The  buildings  of  the  National  Cash  Register 
Company  of  Dayton,  Ohio,  have  so  many  large  windows 
that  they  look  almost  like  glass  structures. 

QUESTIONS    AND    EXERCISES 

1.  Name  the  parts  of  the  eye.     Give  the  use  of  each  part. 

2.  Can  you  see  objects  that  are  black?     Explain. 

3.  Explain  why  the  persons  in  a  moving  picture  show  seem 
to  be  moving. 

4.  What  are  some  defects  of  the  eye?     What  is  the  remedy 
for  such  defects? 

5.  How  can  improper  use  of   the  eyes   produce   headache? 
Give  the  remedy  for  such  a  headache. 

6.  Make  some  general  statements  for  the  care  of  the  eyes. 

7.  What  is  the  relation  between  light  and  health? 


CHAPTER  XXIX 
ARTIFICIAL  LIGHT 

197.  The  First  Artificial  Light. —  Primitive  man  did  not 
have  much  use  for  artificial  light  because  he  did  no  reading 
or  sewing;  he  found  ample  time  during  daylight  to  do  his 
work.     The  open  fire  was  the  first  artificial  light  employed 
by  man.     With  fire  some  of  the  food  was  prepared  and 
the  rude  dwelling  places  were  lighted.     Man  then  learned 
to  carry  a  burning  piece  of  wood  while  going  about  in  dark 
caves  or  at  night.     Pine  wood  or  wood  dipped  in  animal 
oil  or  fat  served  well  for  this  purpose.     By  experimenting 
with  animal  oil  man  found  that  it  could  be  molded  into 
sticks  with  some  kind  of  a  substance  in  the  center  to  serve 
as  a  wick.     As  with  all  inventions  it  took  many  years  for 
the  candle  to  be   perfected.     The   candle  was  used  for 
several  thousand  years  without  much  improvement  or 
modification   except   in    the    method    by   which   it   was 
made. 

198.  Oil  and  Gas. —  During  this  long  period  of  man's 
improvement  of  artificial  lighting  from  the  discovery  of 
fire  to  the  perfected  candle,  and  during  many  millions 
of  years  before  this,  there  were  being  formed  in  the  earth 
large  quantities  of  petroleum,  gas,  and  coal.     These  were 
formed  of  plant  and  animal  matter  which  was  deeply 
buried  millions  of  years  ago  by  the  deposit  of  sand  and 
clay  which  was  carried  by  flowing  water  from  the  highlands 
into  the  low  and  swampy  places  and  by  the  rising  and 
sinking  of  the  crust  of  the  earth.     It  was  not  until  recent 


290  GENERAL  SCIENCE 

times  that  man  discovered  petroleum,  coal,  and  gas,  and 
learned  how  to  get  them  out  of  the  earth  and  use  them. 
During  the  latter  half  of  the  nineteenth  century  and  the 
beginning  of  the  twentieth  century,  methods  of  artificial 
lighting  have  progressed  by  leaps  and  bounds.  The 
candle  was  rapidly  replaced  with  the  oil  lamp,  which  was 
at  first  very  imperfect  and  dangerous  because  the  gasoline 
could  not  be  removed  from  the  oil  and  hence  lamps  would 
occasionally  explode.  Improvements  were  made  in  the 
lamp  and  in  the  refining  of  the  petroleum  until  it  made 
an  almost  ideal  light. 

The  discovery  of  natural  gas  led  to  the  invention  of  a 
gas  lamp  which  was  used  extensively  in  regions  where 


i 

ACETYLENE  BURNER  AND  FLAME 
Air  enters  the  openings  at  B. 

gas  was  found.  Gas  lights  were  more  convenient  and 
less  expensive  than  oil  lamps.  After  the  discovery  of 
how  to  make  gas  out  of  coal,  the  gas  lamp  came  into 
common  use  wherever  coal  could  be  secured  at  reasonable 
rates.  The  natural  and  coal  gases  were  also  used  for  cook- 
ing and  heating  after  gas  stoves  were  invented.  Acetylene 
gas,  a  compound  of  carbon  and  hydrogen,  is  burned  in 
the  same  kind  of  lamp  as  other  gases.  Vaporized  gasoline 
"is  also  much  used  for  lighting,  being  burned  in  gas  lamps. 
After  the  invention  of  machinery  that  would  generate 
an  electric  current,  electric  lights  soon  came  into  use. 
With  the  improvements  that  have  been  made  on  the  first 


ARTIFICIAL  LIGHT 


291 


D— 


electric  light,   it  has  become  the  most  convenient  and 
effective  method  of  lighting. 

199.  How  Lamps  Make  Light. —  Before  animal  oils  or 
carbon  oils  can  burn  in  a  flame,  they  must  be  vaporized, 
that  is,  changed  into  a  gas.  The  flame  on  the  wick  of 
a  tallow  candle  melts  the  tallow.  The  liquid  tallow  is 
drawn  up  the  wick  and  evaporated.  The 
flame  raises  this  vapor  to  the  kindling  point, 
at  which  temperature  the  carbon  and  hy- 
drogen unite  with  the  oxygen.  The  small 
carbon  particles,  as  they  unite  with  the 
oxygen,  become  so  hot  that  they  are  self- 
luminous.  These  glowing  particles  of  car- 
bon in  the  flame  of  the  candle  are  the 
light-producing  part  of  the  flame.  If  the 
flame  is  cooled  slightly  by  blowing  at  it,  a 
black  smoke  will  come  from  it.  This  smoke 
is  composed  of  unburned  carbon.  CANDLE  FLAME 

The  light  of  a  carbon  oil  lamp  is  made       A,  combustible 

,  .  ,  ,  •  i        i  gases    from    the 

by  the  glowing  white  carbon  particles  dur-    meited  candle, 
their    oxidation.     The   carbon   oil    is    &>  bluish  flame. 

C,      luminous 


ing 


vaporized  as  it  gets  to  the  top  of  the  wick,  flame.  D,  hottest 
If  the  burner  of  a  lamp  is  not  clean,  not  mo^lnvSe^" 
enough  air  can  pass  through  the  holes 
below  the  flame  and  the  vaporized  oil  cannot  get  suf- 
ficient oxygen  for  complete  oxidation;  the  result  is  that 
the  lamp  smokes  and  poisonous  gases  come  from  it.  If  the 
wick  is  turned  too  high,  not  enough  oxygen  can  enter  the 
burner  to  oxidize  the  gas  and  smoking  also  results.  A 
good  oil  lamp,  well  cared  for,  will  not  produce  any  smoke 
or  bad  odor,  but  will  make  a  good  light. 

Gas  lamps  with  a  broad,  open  flame  make  light  in  the 
same  way  as  the  oil  lamp,  namely,  by  the  glowing  par- 


292  GENERAL   SCIENCE 

tides  of  carbon  during  their  oxidation.  The  gas  lamps 
which  use  some  type  of  the  Bunsen  burner  have  a  mantle 
over  the  flame.  The  Bunsen  burner  mixes  the  oxygen 
of  the  air  with  the  gas  before  it  gets  to  the  flame,  and 
complete  oxidation  of  the  carbon  particles  occurs  so 
quickly  that  not  much  light  is  produced,  but  a  very  hot 
flame  results.  This  flame  brings  the  white  mantle  to  a 
glowing  white  heat  and  a  very  bright  light  is  produced. 
The  Bunsen  burner  can  be  used  for  burning  gasoline, 
acetylene  gas,  or  natural  gas. 

Incandescent  electric  light  bulbs  make  light  because  the 
fine  wire,  carbon,  or  tungsten  filament  in  them  is  made 
white-hot  by  the  electric  current  passing  through.  In  the 
street  corner  arc  light  a  glowing  arc  of  white-hot  carbon 
vapor  and  the  glowing  ends  of  the  carbon  make  the  light. 
There  are  two  sticks  of  carbon  in  the  lamp,  and  after  the 
current  is  turned  on  the  ends  of  the  carbon  are  automat- 
ically pulled  apart  and  then  the  electric  current  crosses  from 
one  to  the  other  by  vaporizing  the  carbon.  While  the 
carbon  is  being  vaporized,  it  is  made  white-hot.  The  arc 
lamps  can  be  made  to  give  a  light  of  500  candle  power. 

200.  Illuminating  Substances.  —  Candles  are  made  of 
tallow,  sperm  whale  oil,  or  paraffin,  by  dipping  the  wicks 
into  the  melted  oil  or  by  pouring  it  into  molds  containing 
the  wicks. 

Carbon  oil  and  gasoline  are  made  by  distilling  crude 
petroleum.  Paraffin  is  also  obtained  from  petroleum. 

Natural  gas  is  obtained  by  drilling  into  the  earth  in 
the  same  manner  as  for  petroleum  and  then  collecting 
the  gas  in  storage  tanks,  from  which  it  is  piped  to  buildings 
for  heating,  cooking,  and  lighting.  Natural  gas  is  not 
very  widely  distributed  and  its  use  is  largely  restricted 
to  the  regions  where  it  is  found. 


ARTIFICIAL  LIGHT  293 

Artificial  or  coal  gas  is  made  by  heating  coal  in  fur- 
naces where  air  or  oxygen  cannot  get  to  it.  The  gas  comes 
from  the  coal  containing  many  impurities  which  are  re- 
moved by  washing  the  gas,  that  is,  by  passing  it 
through  water  and  other  substances;  the  pure  gas  is 
then  collected  in  tanks  for  use.  The  by-products  which 
come  from  the  production  of  coal  gas  are  ammonia,  coal 
tar,  carbolic  acid,  naphthalene,  and  anilin  dye.  Coke  is 
the  residue  left  after  the  gas  is  driven  out  of  the  coal. 

Acetylene  gas  is  made  by  allowing  calcium  carbide 
crystals  to  fall  continuously  into  a  tank  containing  water. 
The  tank  is  air-tight  and  so  arranged  that  the  inside  part 
can  move  up  and  down  according  to  the  gas  pressure. 
The  gas  is  distributed  through  pipes  to  the  burners.  In 
acetylene  gas  lamps  the  water  is  permitted  to  drip  into 
the  can  containing  the  calcium  carbide.  The  carbide  is 
made  by  fusing  coal  and  lime  together  in  an  electric 
furnace.  Slaked  lime  is  the  residue  left  after  acetylene 
gas  is  made  by  the  action  of  water  on  the  carbide. 

QUESTIONS    AND    EXERCISES 

1.  Give  the  history  of  the  development  of  artificial  lighting. 

2.  How  are  oil  and  gas  obtained  for  lighting? 

3.  Have  oil  and  gas  always  been  used? 

4.  Explain  how  a  gas  flame  makes  light. 

5.  Explain  how  an  electric  lamp  makes  light. 

6.  What  are  the  substances  now  used  for  lighting? 


CHAPTER  XXX 
SOUND 

201.  Personal  Experiences.  —  We  have  not  been  in  this 
world  very  long  before  we  have  been  attracted  by  a  sensa- 
tion received  through  the  ears  and  have  also  attracted 
the  attention  of  those  about  us  by  our  voices.  We  grow 
able  to  produce  sounds  which  are  loud  or  soft  according 
to  our  wish.  When  we  gain  the  ability  to  carry  a  tune, 
we  are  able  not  only  to  distinguish  one  tone  from  another 
as  having  a  different  pitch,  but  also  to  produce  tones  of 
a  different  pitch.  We  then  soon  learn  to  note  the 
difference  in  the  character  of  a  tone  produced  by  a  piano 
and  a  violin,  a  violin  and  a  guitar,  or  a  piano  and 
the  human  voice.  We  discover  the  echo  as  we  walk 
heavily  in  a  large  hall  or  speak  loudly  when  at  the  proper 
distance  from  a  large  building  or  steep  hillside. 

During  early  youth  we  discover  that  the  shrill  whistle 
of  a  locomotive  or  other  steam  engine  is  produced  by  the 
emission  of  steam,  and  if  we  are  at  some  distance  from 
the  locomotive  we  see  the  steam  a  few  seconds  before 
we  hear  the  whistle;  so  we  conclude  that  it  requires  time 
for  sound  to  travel  over  the  space  between  us  and  the 
locomotive.  The  time  arrives  when  we  no  longer  have 
any  difficulty  in  distinguishing  between  a  noise  and  a 
musical  sound;  and  when  several  tones  of  different  pitch 
are  sounded  together,  we  soon  decide  whether  the  effect 
is  harmonious  and  pleasant  or  whether  it  is  a  discord. 

The  foregoing  are  some  of  the  experiences  that  we  pass 


SOUND 


295 


VIBRATIONS  OF  A  ROD 


through  while  growing  from  childhood  to  maturity.     It 

is  the  aim  of  this  chapter  to  present  some  definite  ideas 

concerning  the  nature  and  cause  of  the  experiences  which 

we  have   had.     We   have  found   that  we  can  not  only 

distinguish  sounds  from  each  other, 

but  that  we  can  also  ascertain  the 

direction  from  which  most  sounds 

come.     The  ability  to  determine 

the  direction  enables  us  to  locate 

the  source   or    the    cause   of   the 

sound.     Every  time  we   look  for 

the  cause  we  find  some  vibrating 

body  or  an  object  that  has  been 

vibrating. 

202.  Sound  Caused  by  Vibra- 
tions.— When  the  bow  is  drawn  across  one  of  the  strings 
of  a  violin,  that  string  will  emit  a  tone  and  it  can  be  easily 
seen  that  the  string  is  moving  or  vibrating  back  and  forth 
very  rapidly.  The  string  has  a  hazy 
appearance  because  the  eye  can  detect 
only  about  ten  separate  objects  or  mo- 
tions per  second.  The  violin  string 
vibrates  many  times  ten  per  second  and 
so  appears  to  have  a  hazy  width.  If  a 
piece  of  steel  or  a  ruler  is  clamped  in  a 
vice  or  held  firmly  on  the  edge  of  a  desk 
and  then  made  to  vibrate,  a  tone  will  be 
produced.  That  the  ruler  is  vibrating 
can  easily  be  seen.  When  the  vibration 
ceases  no  sound  can  be  heard.  The 
prongs  of  a  tuning  fork  also  look  hazy  at  the  end  when  a 
tone  is  given  out.  To  prove  that  the  fork  is  vibrating 
when  it  emits  a  tone,  touch  some  water  with  the  ends  of 


TUNING  FORK 

The  vibrating  fork 
throws  the  water. 


296  GENERAL  SCIENCE 

the  prongs,  as  shown  in  the  illustration,  and  see  if  the  fork 
throws  the  water.  From  these  tests  we  can  conclude 
that:  Sound  is  caused  by  a  vibrating  body.  If  the  strings 
of  a  violin,  guitar,  or  piano  are  struck,  a  sound  is  made. 
If  an  explosion  of  gas  or  powder  occurs,  the  air  is  made  to 
vibrate  and  we  hear  the  sound.  If  a  book  or  pencil  falls 
on  the  floor,  the  floor  is  made  to  vibrate  and  a  sound  is 
produced.  If  some  one  taps  on  the  door,  desk,  table,  or 
even  the  brick  wall,  these  objects  will  be  made  to  vibrate 
and  a  sound  may  be  heard. 

203.   Transmission  of  Sound. —  Every  part  of  our  body 
is  sensitive  to  the  vibratory  motion  of  a  solid  body  which 


SHOWING  SOUND  WAVES  IN  THE  AIR 

touches  us;  but  our  ears  are  the  special  organs  for  de- 
tecting sound,  and  they  are  sensitive  to  very  slight 
vibratory  motions.  No  sensation  of  sound  can  be  re- 
ceived unless  the  inner  parts  of  the  ears  are  disturbed  by 
a  vibrating  substance.  Since  air  touches  our  ears  all  the 
time,  it  is  the  most  common  substance  which  carries 
the  vibrations  of  a  distant  object  to  us.  But  air  is  not 
the  only  substance  that  will  carry  sound.  The  Indians 
put  their  ears  to  the  ground  to  hear  a  distant  noise. 
An  approaching  train  can  easily  be  -heard  by  placing  the 
ear  or  teeth  on  the  steel  rail  of  the  track.  The  sound  of 
the  electric  car  is  carried  by  the  trolley  wire.  If  two 
stones  are  struck  together  under  water,  the  sound  can 


SOUND  297 

be  heard  a  considerable  distance  away  by  a  person  whose 
ears  are  in  the  water.  These  facts  show  that  sound  can 
be  carried  from  its  source  to  the  ear  by  solids,  liquids,  or 
gases. 

204.  Speed  of  Sound. —  In  our  rooms  during  conversa- 
tion we  might  suppose  that  sound  travels  instantly  from 
one  person  to  another.     But  when  we  see  the  condensed 
steam  from  the  whistle  of  a  locomotive  evaporate  or  be- 
come invisible  before  we  hear  the  sound,  we  know  that 
sound  does  not  travel  instantly.     If  we  see  a  flash  of  light- 
ning, it  is  sometimes  several  seconds  before  we  hear  the 
thunder. 

The  French  Academy  of  Science  appointed  a  com- 
mission in  1832  to  determine  the  speed  of  sound.  They 
placed  cannon  on  two  hilltops  that  were  11.5  miles  apart. 
The  cannon  were  fired  at  night  so  that  the  flash  could 
be  seen,  and  the  time  was  determined  from  the  time  the 
flash  was  seen  till  the  sound  was  heard.  This  commis- 
sion found  the  speed  of  sound  to  be  331.2  meters  per 
second,  when  the  air  was  at  freezing  temperature  or  o°  C. 
The  accepted  rate  for  the  speed  of  sound  is  331.3  meters, 
or  1087  feet,  per  second  at  o°  C.  The  speed  of  sound  in 
water  is  1400  meters  per  second,  or  about  four  times  the 
speed  in  air.  The  speed  in  iron  is  5100  meters  per  second, 
or  about  sixteen  times  the  speed  in  air. 

The  speed  of  sound  in  air  increases  with  an  increase  in 
temperature.  The  amount  of  this  increase  is  about  60 
centimeters,  or  two  feet,  per  second  per  degree  centigrade. 
So  the  speed  of  sound  at  20°  C.  is  40  feet  per  second 
more  than  at  o°  C.,  or  the  speed  at  20°  C.  is  about  343.3 
meters,  or  1126  feet,  per  second. 

205.  Reflection   of    Sound. —  An   echo   is   a   reflected 
sound.     All  solid  objects  reflect  sound  just  as  nearly  all 


298 


GENERAL  SCIENCE 


reflect  light.  The  objects  which  diffusely  reflect  light  we 
can  see,  while  those  with  smooth  surfaces,  like  a  mirror, 
reflect  light  so  perfectly  that  we  see  images  of  objects 
instead  of  the  mirror  itself.  In  a  sense  the  opposite  is 
true  with  sound.  The  objects  which  are  so  rough  that 
they  reflect  sound  diffusely  do  not  make  an  echo,  be- 
cause the  sound  wave  is  broken  up  and  reflected  in  all 

directions  to  such  an  ex- 
tent that  no  distinct 
wave  returns  to  our  ears. 
Buildings  and  most  rock 
cliffs  and  steep  hillsides 
are  smooth  enough  to 
reflect  sound  and  make 
an  echo.  If  we  make  a 
loud  sound  about  one- 
eighth  of  a  mile  from  a 
large  building  or  hill, 
the  echo  will  be  heard 

in  about  a  second.  If  we  are  only  fifty  feet  from  the  re- 
flector, we  will  not  get  a  good  echo  because  the  sound 
wave  will  return  in  less  than  a  tenth  of  a  second.  The 
human  ear  cannot  distinguish  more  than  about  ten  dis- 
tinct sounds  per  second.  If  eleven  or  twelve  sounds  per 
second  are  made,  they  will  seem  to  the  human  ear  like 
one  continuous  sound. 

In  a  hall  or  large  auditorium  the  speaker's  voice  is 
reinforced  by  the  reflections  of  the  sound  from  the  walls. 
Since  the  reflected  sound  and  the  sound  direct  from  the 
speaker's  voice  strike  our  ears  so  nearly  at  the  same  time, 
we  are  unable  to  distinguish  any  echo,  but  we  get  a  louder 
sound  than  if  there  were  no  reflection.  A  speaker  in  the 
open  air  must  talk  with  a  much  louder  voice  than  in  a 


SOUND  REFLECTOR  FOR  AN  ORCHESTRA 


SOUND  299 

building,  or  he  could  not  be  heard  very  far.  Why? 
Sometimes  auditoriums  are  built  in  such  a  form  that  the 
walls  reflect  the  sound  back  and  forth,  and  the  sound 
waves  from  the  speaker  are  so  disturbed  that  he  cannot 
be  heard  distinctly.  This  defect  of  auditoriums  can  be 
remedied  sometimes  by  stretching  wires  across  the  hall 
or  by  hanging  draperies,  or  by  moving  the  stage  toward 
the  audience. 

Sometimes  an  echo  is  produced  when  a  sound  wave 
passes  from  one  layer  of  air  to  another  layer  of  greater 
density.  Sound  will  also  be  reflected  when  it  passes  from 
one  current  of  air  into  another  current  going  in  the  op- 
posite direction.  The  rumbling  noise  following  a  thunder- 
clap is  due  to  the  reflection  of  the  sound  by  the  clouds 
and  air. 

QUESTIONS   AND   EXERCISES 

1.  Recall  all  your  experiences  with  sound  and  write  what 
you  know  about  it. 

2.  How  is  sound  made? 

3.  How  is  sound  carried?     How  fast? 

4.  Can  sound  be  reflected? 

5.  Explain  the  echo. 

6.  What  practical  use  is  made  of  sound? 


CHAPTER  XXXI 
VOCAL  CORDS  AND   THE  EARS 

206.  Vocal  Cords. —  The  vocal  cords  are  the  organs 
which  produce  sounds  for  speech.  They  are  two  tough, 
elastic  bands,  stretched  across  the  upper  end  of  the 
windpipe,  and  their  ends  are  attached  to  the  cartilage 
of  the  larynx  (Adam's  apple).  These  cords  can  be  ren- 


Cords  stretched  for  singing.  Cords  as  they  are  for  breathing. 

HUMAN  VOCAL  CORDS 

dered  more  or  less  tense  by  muscles  which  by  contraction 
can  move  the  pieces  of  cartilage.  When  we  speak  or  sing, 
these  muscles  stretch  the  cords  and  make  the  passage 
between  them  small,  so  that  when  the  air  from  the  lungs 
is  forced  out  between  the  cords,  they  vibrate  and  produce 
sounds  called  the  voice.  The  pitch  of  the  voice  depends 
upon  the  number  of  vibrations  per  second  of  the  vocal 
cords.  When  these  sounds  are  modified  by  certain  posi- 
tions of  the  tongue,  palate,  teeth,  lips,  and  nose,  so  as 
to  form  words,  speech  is  produced. 

The  vocal  cords  are  longer  in  men  than  in  women  and 
therefore  women  have  a  voice  of  higher  pitch.  The  longer 
and  thicker  the  cords  are,  the  less  frequently  they  vibrate 


VOCAL  CORDS  AND  THE  EARS        301 

when  air  is  forced  out  between  them.  Because  of  this 
difference  between  the  vocal  cords  of  men  and  women, 
men  cannot  sing  such  high  notes  as  women,  and  women 
cannot  make  the  low  tones  of  the  bass.  A  man's  voice 
is  about  one  octave  lower  than  a  woman's  voice.  The 
voice  of  a  boy  has  the  same  pitch  as  that  of  a  girl.  A  boy's 
voice  drops  one  octave  between  the  ages  of  14  and  18  years. 
The  difference  between  a  soprano  and  an  alto  voice  is 
merely  one  of  length,  tension,  and  thickness  of  the  vocal 
cords.  The  difference  between  a  tenor  and  a  bass  voice 
is  caused  by  the  same  variations. 

The  loudness  of  the  voice  depends  upon  the  force  with 
which  the  cords  vibrate,  and  this  depends  upon  the  force 
with  which  the  air  is  expelled  from  the  lungs  when  passing 
between  the  cords.  While  whispering  the  vocal  cords  are 
so  far  apart  that  the  small  amount  of  air  passing  through 
does  not  make  them  vibrate,  but  the  current  of  air  is 
checked  at  intervals  and  modified  by  the  organs  of  speech. 

207.  The  Voice. —  The  quality  of  the  human  voice  is 
determined  principally  by  the  condition  of  the  chest, 
windpipe,  mouth,  and  nose.  The  air  in  these  organs  is 
caused  to  vibrate  by  the  vocal  cords.  The  nasal  twang 
is  produced  when  the  nasal  passages  are  partly  or  com- 
pletely closed  by  a  cold  or  by  a  growth  of  tissue  called 
adenoids.  Hoarseness  is  due  to  a  swelling  of  the  cords, 
resulting  from  the  blood  and  lymph  (a  colorless  liquid) 
collecting  in  them  because  of  a  cold  or  too-long-continued 
use.  To  train  the  voice,  then,  is  to  remove  all  these 
needless  obstructions,  to  learn  how  to  control  the  action 
of  the  cords  and  make  them  respond  at  will,  and  to  de- 
velop the  resonant  parts  so  that  the  qualities  of  beauty 
and  clearness  will  be  gained.  It  is  important  that  every- 
one should  cultivate  a  smooth  and  pleasant  tone  of  voice. 


302 


GENERAL   SCIENCE 


The  mouth  should  be  well  opened  while  speaking  or  sing- 
ing, the  soft  palate  elevated,  and  the  lips  moved  with 
firmness.  A  mouth-breather  can  never  develop  a  clear, 
sweet  voice,  because  the  vocal  cords  are  affected  by  the 


Branches 
$f  aii  di  Lory 


Cochlea 


Eustachfon 

^ ,.___"        tube 

DIAGRAM  or  SECTION  THROUGH  THE  HUMAN  EAR 

cold  air  and  dust  which  reach  them  by  such  breathing. 
A  person  who  has  not  learned  to  breathe  through  the  nose 
cannot  sing  or  speak  very  long  without  becoming  hoarse. 
The  teeth  also  play  an  important  part  in  singing  and  speak- 
ing by  their  resonant  and  modulating  effect.  To  have  a 
good  voice  for  singing,  good  teeth  are  usually  necessary. 

208.  The  Ears. —  The  ear  consists  of  three  principal 
parts,  namely,  the  external  ear,  the  middle  ear,  and  the 
internal  ear.  The  external  ear,  which  is  visible  on  the 
side  of  the  head,  is  more  or  less  folded  so  that  it  can 
catch  the  sound  waves  and  reflect  them  toward  or  into 
the  ear-tube,  called  the  auditory  canal,  which  is  about 
an  inch  long.  The  inner  end  of  this  canal  is  closed  by 
a  membrane  called  the  tympanic  membrane  or  ear- 


VOCAL  CORDS  AND  THE  EARS        303 

drum.  The  ear-drum  is  a  thin,  membrane-like  muscle 
which  vibrates  when  a  sound  strikes  it. 

The  middle  ear  is  separated  from  the  external  ear  by 
the  ear-drum  and  is  connected  with  the  throat  by  a  tube 
called  the  Eustachian  tube,  through  which  air  can  pass 
in  and  out  of  the  middle  ear.  Air  comes  out  of  the  Eus- 
tachian tube  when  the  air  pressure  in  the  outer  ear  de- 
creases, and  air  goes  into  the  tube  when  the  air  pressure 
outside  increases.  The  purpose  is  to  keep  the  air  pres- 
sure in  the  middle  ear  the  same  as  in  the  outer  ear,  in 
order  that  the  ear-drum  may  keep  its  position  and  not 
bulge  in  or  out,  or  be  burst.  The  middle  ear  also  has 
three  small  bones  called  the  hammer,  anvil,  and  stirrup, 
which  form  a  chain  from  the  ear-drum  to  a  membrane 
closing  an  oval  opening  into  the  internal  ear.  These 
bones  transmit  the  vibrations  of  the  ear-drum,  caused  by 
sound  waves,  to  the  membrane  of  the  inner  ear. 

The  inner  ear  is  composed  of  several  irregular  connected 
cavities.  The  three  semicircular  canals,  at  right  angles 
to  each  other,  have  nothing  to  do  with  hearing,  but  enable 
the  body  to  keep  its  balance  and  know  its  position  even 
with  the  eyes  closed.  The  coiled  part  of  the  inner  ear, 
called  the  cochlea  because  it  resembles  a  snail  shell,  con- 
tains a  watery  fluid  and  also  the  ends  of  the  nerves  of 
hearing.  This  fluid,  when  disturbed  by  sound  waves, 
affects  the  hair-like  parts  which  connect  with  the  nerves. 

209.  Hearing. —  When  an  explosion  or  a  vibrating  body 
produces  a  sound  wave,  the  outer  visible  part  of  the  ear 
reflects  the  wave  into  the  auditory  canal.  The  ear-drum 
is  made  to  vibrate  and  the  three  bones  in  the  middle  ear 
carry  this  vibratory  motion  to  the  membrane  of  the  inner 
ear.  The  liquid  in  the  inner  ear  transmits  the  vibrations 
to  the  hair-like  projections  of  the  cells  containing  the 


304  GENERAL  SCIENCE 

nerves  of  hearing.  The  nerve  fibers  unite  to  form  the 
auditory  nerve  which  carries  the  stimulus  to  the  brain. 
The  brain  interprets  it  in  relation  to  loudness,  quality, 
pitch,  the  direction  from  which  it  came,  and  the  distance 
of  its  origin.  From  these  characteristics,  in  the  light  of 
previous  knowledge  and  experience,  the  origin  and  cause 
of  the  sound  may  be  ascertained. 

210.  Care  of  the  Ears. —  Hard  objects,  such  as  pencils, 
toothpicks,  and  matches,  should  not  be  pushed  into  the 
auditory  canal  of  the  outer  ear  for  fear  of  puncturing  the 
ear-drum.  The  wax,  which  keeps  insects  and  dirt  out 
of  the  ear,  sometimes  collects  in  too  large  quantities  and 
hardens  in  the  canal.  It  can  be  removed  with  the  round 
end  of  a  hairpin  by  being  careful  not  to  shove  the  hairpin 
in  more  than  about  three-fourths  of  an  inch.  The  hard- 
ened wax  can  also  be  softened  by  the  use  of  warm  water 
and  then  easily  removed.  A  person  should  never  be 
struck  upon  the  ear  with  the  open  hand,  because  the  ear- 
drum may  be  injured  by  the  air  which  is  suddenly  forced 
into  the  auditory  canal  by  the  swiftly  moving  hand.  The 
Eustachian  tube  is  sometimes  closed  at  the  throat  end 
during  the  time  when  a  person  has  a  cold,  and  then  the 
air  pressure  in  the  middle  ear  cannot  be  kept  the  same 
as  it  is  in  the  outer  ear;  this  may  result  in  the  rupture 
of  the  ear-drum  and  deafness  may  follow.  To  keep  the 
ears  in  good  condition  one  should  guard  against  all  nose 
and  throat  diseases. 

QUESTIONS  AND  EXERCISES 

1.  Where  are  the  vocal  cords?     Of  what  use  are  they? 

2.  What  parts  of  the  body  affect  the  voice?     How  is  nasal 
speech  produced? 

3.  Name  the  parts  of  the  ear  and  the  use  of  each. 

4.  How  do  colds  and  throat  diseases  affect  the  ears?     How 
should  you  care  for  the  ears? 


CHAPTER  XXXII 
THE  SOIL 

211.  The  Soil  is  the  surface  of  the  earth  which  con- 
tains  the   necessary  compounds   and   characteristics   for 
the  growth  of  plants.     It  varies  in  depth  from  a  few 
inches  to  many  feet,  according  to  the  method  of  forma- 
tion and  the  amount  of  erosion  that  has  taken  place.     It 
can  be  increased  in  depth  by  the  growth  of  vegetation  and 
by  proper  cultivation. 

212.  Origin. —  The  surface  of  the  earth  at  one  time  was 
barren   rock,    unfit   for   plant   or    animal   life.     It   was 
much  like  the  surface  of  cooled  lava  which  flowed  from 
volcanos.     There  are  yet  in  the  Rocky  Mountain  section 
large  areas  of  almost  barren  rock  which  are  not  suitable 
for  cultivation.     Some  other  parts  of  the  earth  are  covered 
with  vast  lava  flows  which  cannot  be  cultivated,  and  no 
plants  of  any  kind  can  grow  on  them. 

The  surface  of  the  rock  which  ages  ago  covered  the  earth 
was  gradually  broken  up  or  decomposed  by  the  action  of 
water,  air,  and  the  changes  of  temperature  from  one 
season  to  another.  The  oxygen  of  the  air  oxidized  the 
iron  and  certain  other  substances  that  it  could  reach,  and 
the  water  made  it  more  favorable  for  this  oxidation  to 
occur.  You  know  that  iron  if  wet  will  rust  rapidly,  that 
is,  it  will  oxidize.  The  water  dissolved  parts  of  the  rock 
and  carried  insoluble  particles  into  localities  where  they 
were  deposited  with  the  soluble  parts  left  by  the  water 
when  it  evaporated.  The  expansion  and  contraction  of 


3o6  GENERAL   SCIENCE 

the  rock  caused  by  the  changes  in  temperature  made  the 
rock  crumble  into  fine  particles.  The  freezing  of  water  in 
the  rock  greatly  assisted  this  crumbling  process. 

Small  quantities  of  this  disintegrated  rock  collected  in 
various  places  and  made  it  possible  for  the  lowest  plant 
forms  to  begin  life.  The  decomposed  rock  contained  the 
necessary  chemical  elements  for  primitive  plant  growth. 


BENEATH  THE  SOIL  is  ROCK 

As  these  simple  plant  forms  grew  to  maturity  and  died, 
they  added  decaying  plant  matter  to  the  forming  soil. 
This  decaying  matter,  as  soon  as  it  became  soluble,  served 
as  food  for  other  plants.  Then  came  a  process  of  plant 
changes,  or  the  evolution  of  plants.  As  plant  food  be- 
came more  abundant,  the  simple  plants  grew  larger  and 
more  complex  in  their  structure.  They  decomposed  the 
rock  with  their  roots,  took  food  from  the  air  with  their 
leaves,  and  then  in  turn  died  and  decayed;  thus  the  soil 
was  increased  in  depth  and  richness.  This  process  con- 
tinued for  ages,  and  now  the  larger  part  of  the  land  sur- 
face of  the  earth  is  able  to  support  plant  life  of  some  type. 
Since  man  has  been  growing  plants  for  food  many  rich 


THE  SOIL  307 

soils  have  been  ruined  by  ignorance  and  carelessness. 
In  recent  years  farmers  have  begun  to  learn  how  to  make 
soils  productive  and  how  to  keep  them  fertile. 

213.  Physical  Composition  of  the  Soil. —  In  the  preced- 
ing section  is  given  the  origin  of  two  of  the  important 
parts  of  a  productive  soil.  The  greater  portion  by  weight 
of  most  soils  is  composed  of  decomposed  rock  or  rock 
particles,  but  no  crop  could  grow  on  a  soil  composed  en- 


A  HILLSIDE  PROPERLY  CULTIVATED  TO  PREVENT  EROSION 

tirely  of  distintegrated  rock.  A  soil  which  is  suitable  for 
agricultural  purposes  is  made  up  of  five  important  parts, 
namely,  (i)  disintegrated  rock,  (2)  soil  water,  (3)  soil 
air,  (4)  humus  or  decaying  organic  matter,  and  (5)  bac- 
teria and  other  living  organisms. 

Not  many  kinds  of  crops  can  be  produced  in  soil  which 
lacks  any  one  of  these  five  parts.  Much  soil  which  is 
found  in  some  swampy  regions  is  made  up  largely  of  de- 
caying organic  matter.  It  is  valuable  for  growing  onions 
and  celery.  Soils  that  do  not  have  the  proper  amounts 
of  water,  air,  bacteria,  or  humus,  will  not  grow  large  crops. 


3o8  GENERAL  SCIENCE 

214.  Disintegrated  Rock. —  All  rock  on  the  earth  was 
at  one  time  igneous  like  that  which  flows  from  active 
volcanos.  This  igneous  rock  was  acted  upon  by  the  heat 
of  the  sun,  by  water,  and  by  the  air  until  it  was  broken 
up  so  that  the  flowing  water  could  carry  the  finer  particles 
and  some  in  a  soluble  form.  These  deposits  of  disinte- 
grated rock  made  by  the  water  sometimes  became  deep 
enough  so  that  they  turned  into  solid  rock  again.  The 
rock  dissolved  in  the  water  served  to  cement  the  sand 
and  gravel  together  the  same  as  when  cement  is  used  for 
making  concrete. 

Sand  rocks  were  made  mostly  of  sand  cemented 
together.  The  kind  of  sand  rock  was  determined  largely 


LIMESTONE  MADE  OF  SHELLS 

by  the  size  of  the  sand  grains  and  their  chemical  com- 
position. Lime  rock  was  formed  from  the  shells  of 
water  animals.  At  one  time  these  animals  with  shells 
for  protection  were  more  numerous  than  any  other  kind, 
and  as  they  died  their  shells  formed  deposits  many  feet 
deep  in  the  part  of  the  ocean  in  which  they  lived.  After 
many  feet  of  sand  and  clay  were  deposited  on  the  top  of 
these  shells  they  were  pressed  together  so  solidly  that  they 
formed  stone,  which  is  our  present  limestone.  Limestone 
could  be  made  of  oyster,  clam,  and  muscle  shells  because 
they  have  the  same  chemical  composition  as  limestone. 
Chalk  is  a  form  of  limestone  made  of  very  small  shells 
of  animals  which  lived  in  the  water  by  millions.  If  chalk 


THE  SOIL 


309 


dust  is  placed  under  the  microscope  the  individual  shells 
can  be  seen.  The  extensive  chalk  deposits  in  the  United 
States  and  England  were  formed  of  these  tiny  animals. 

The  marble  of  the  New  England  States  was  made 
by  the  limestone  deep  in  the  earth  being  heated 
to  a  certain  temperature  and 
then  cooled;  afterward  the  sand 
rock  on  top  of  it  was  washed 
away  and  the  marble  was  ex- 
posed to  view  and  now  man  can 
quarry  it  for  building  purposes. 

The  formation  of  sand  rock 
from  water  deposits,  limestone 
from  deposits  of  shells,  and  with 
a  deposit  of  clay  occasionally 
between  the  rock  layers,  has 
gone  on  for  millions  of  years, 
so  that  now  rock  strata  formed 
of  water  deposits  are  many  miles 
deep.  During  all  these  past 
ages  the  earth  was  being  pre- 
pared for  the  habitation  of  man,  who  has  now  studied  the 
structure  and  composition  of  the  various  kinds  of  rocks 
and  has  learned  their  relation  to  soils  and  agriculture. 

The  disintegration  of  all  kinds  of  rock  near  the  earth's 
surface  is  still  going  on  and  soil  is  being  formed.  By 
a  knowledge  of  the  kind  of  rock  on  the  surface  in  any 
locality,  one  can  tell  much  of  the  nature  of  the  soil  and 
what  should  be  done  to  make  it  fertile  and  keep  it  pro- 
ductive. A  region  that  has  limestone  near  the  surface 
is  usually  very  productive,  while  the  soils  in  sandstone 
regions  are  not  very  fertile.  It  is  very  expensive  to  make 
sandy  and  clay  soils  fertile  in  a  hilly  or  rolling  country; 


CHALK 

Magnified. 


310  GENERAL  SCIENCE 

but  a  soil  made  of  a  mixture  of  sand  and  clay  in  low  ground 
or  in  river  valleys  can  easily  be  kept  productive. 

The  disintegrated  rock  particles  in  most  soils  make 
from  60  to  95  per  cent  of  the  soil's  weight.  The 
size  of  the  particles  usually  determines  the  nature  and 
productiveness  of  a  soil.  A  coarse-grained  soil  cannot 
retain  much  water,  and  the  spaces  between  the  particles 
are  so  large  that  the  air  can  move  about  in  it  so  freely 
that  much  of  the  soil  water  is  carried  out  by  evaporation. 
This  is  very  noticeable  when  broken  soil  is  not  pulverized 
before  a  dry  season.  Finely  divided  soil  will  retain  the 
water  better.  But  soils  which  hold  a  large  quantity  of 
water  will  not  become  warm  enough  for  the  growth  of 
plants  early  in  the  spring.  The  best  soil  for  general 
purposes  is,  therefore,  one  composed  of  a  mixture  of  coarse 
and  fine  particles. 

215.  Soil  Water. —  Soil  water  is  not  all  the  water  that 
is  in  the  ground,  it  is  only  the  water  which  adheres  to 
the  soil  particles,  like  the  film  of  moisture  which  adheres 
to  an  object  when  it  is  dipped  into  water.  When  soil  is 
moist  and  will  not  pack  if  you  squeeze  it  in  your  hand, 
each  particle  of  it  has  a  film  of  water  around  it.  The  film 
of  water  is  what  the  roots  of  plants  absorb  for  food. 
This  soil  water  has  the  plant  food  dissolved  in  it. 

The  productiveness  of  a  soil  is  usually  determined  by 
the  amount  of  soil  water  which  the  soil  can  hold  and 
by  the  ease  with  which  the  roots  of  plants  can  get  to  this 
soil  water  to  remove  it.  For  this  reason  it  is  very  impor- 
tant that  the  excess  of  water  should  drain  away  during  a 
wet  season  so  that  the  roots  of  plants  can  have  more  soil 
particles  from  which  to  get  food;  and  in  dry  seasons  the 
soil  water  should  not  be  permitted  to  escape  from  the 
surface  by  evaporation.  Excess  water  during  a  wet  sea- 


THE  SOIL  311 

son  can  be  drained  away  by  tiling,  and  evaporation 
during  a  dry  season  can  be  prevented  by  shallow  cultiva- 
tion, thus  forming  a  dust  mulch.  Deep  cultivation  during 
a  wet  season  will  help  to  remove  water  by  evaporation. 
The  farmer  who  learns  how  to  keep  the  .proper  amount 
of  moisture  in  his  soil  is  the  one  who  is  successful  in 
growing  large  crops. 


APPARATUS  TO  TEST  THE  CAPACITY  OP  SOILS  TO  HOLD  WATER 

During  dry  weather  the  water  deep  in  the  ground  comes 
toward  the  surface  by  moving  from  one  particle  of  soil  to 
another,  the  same  as  it  travels  upward  in  a  lump  of  sugar 
or  a  cloth.  Such  a  movement  of  water  is  called  move- 
ment by  capillarity.  This  upward  movement  is  often 
necessary  for  seeds  sown  on  the  surface,  so  that  they  may 
keep  moist  and  grow.  Capillarity  is  assisted  by  running  a 
roller  over  the  ground,  which  crushes  the  clods  and  packs 
the  surface.  This  keeps  the  seeds  moist,  but  the  water 
escapes  by  evaporation.  Sometimes  the  soil  is  packed 
just  over  the  seed,  when  one  or  two  rows  are  planted  at 


312  GENERAL  SCIENCE 

a  time,  as  is  done  by  the  corn  planter,  the  wheels  of  which 
press  the  soil  around  the  grains  of  corn. 

Some  lands  are  too  dry  for  cultivation,  and  so  they  are 
irrigated  by  digging  small  canals  through  which  the 
water  flows  and  seeps  out  into  the  soil,  from  which  the 
plants  take  it  and  the  food  that  is  dissolved  in  it. 

216.  Soil  Air.— About  half  the  volume  of  ordinary 
soils  when  they  are  dry  is  air.  A  cubic  foot  of  dry  soil 
contains  about  half  a  cubic  foot  of  air.  Take  a  known 
quantity  of  dry  soil,  say  one  peck,  and  see  how  much 
water  can  be  poured  into  the  vessel  containing  it.  As  the 
water  goes  in  the  air  comes  out  of  the  soil,  and  hence 
the  quantity  of  water  poured  in  will  be  the  measure  of 
the  air  that  was  in  the  dry  soil.  From  this  it  can  be 
seen  that,  as  the  water  in  soils  increases,  the  amount  of 
air  decreases,  and  that  when  soils  are  saturated  there  is 
very  little  air  in  them.  Soil  air  is  just  as  necessary  for 
the  growth  of  farm  crops  as  it  is  for  the  life  of  animals. 
When  water  excludes  all  the  air  from  the  soil,  the  crops 
will  suffer  and  drown  just  as  surely  as  a  person  drowns 
in  water,  but  not  so  quickly.  This  is  very  noticeable 
when  river  valleys  are  flooded  late  in  the  spring.  Corn 
in  fields  that  were  under  water  for  a  few  days  has  a 
yellowish  color,  while  much  of  the  corn  dies  if  the  soil 
is  covered  with  water  for  a  week  or  more.  Plants  turn 
yellow  when  too  much  water  is  in  the  soil,  because  they 
cannot  then  get  a  sufficient  amount  of  the  element  nitro- 
gen which  is  necessary  for  the  making  of  green  coloring 
matter  in  the  leaf.  Plants  are  not  healthy  without  this 
green  coloring  matter.  Air  is  also  necessary  for  the? 
growth  of  bacteria  in  the  soil.  The  bacteria  decompose 
the  humus  and  leave  it  in  soluble  form  for  the  plants  to 
absorb  with  the  soil  water. 


THE  SOIL  313 

Fine  clay-loam  soils  contain  more  space  for  air  than 
coarse  sandy  soils  because  they  do  not  pack  so  closely, 
the  particles  being  light.  But  the  air  spaces  in  sandy  soils 
are  larger  than  in  finer  soils,  and  this  allows  the  air  to 
move  about  so  freely  in  coarse,  sandy  soils  that  too  much 
water  is  lost  by  evaporation.  Thus  we  see  that  too 
much  air  in  the  soil  is  not  good.  Coarse  soil  is  usually 
too  well  aerated  or  aired  and  also  too  well  drained. 

There  are  some  marsh  plants  that  can  grow  in  standing 
water.  Rice  is  one  of  them,  but  the  common  farm  crops 
could  not  thrive  under  such  conditions.  Even  rice  re- 
quires some  air  in  the  soil,  the  same  as  water  lilies  and 
submerged  seaweeds,  but  these  plants  are  able  to  get  air 
from  the  water.  Ordinary  water  has  a  large  quantity 
of  air  dissolved  in  it. 

217.  Humus. —  Humus  is  the  decaying  plant  and 
animal  matter  of  the  soil.  It  is  composed  of  the  roots 
and  stems  of  dead  plants  and  of  animals  which  died  in 
and  on  the  soil.  Humus  is  organic  matter  and  gives  most 
soils  a  dark  color.  It  is  necessary  for  the  growth  of  good 
crops,  but  the  common  seed-plants  cannot  live  directly  on 
humus.  Plants  can  take  food  from  the  soil  only  in  soluble 
form;  they  cannot  absorb  humus,  but  they  can  take  up 
the  soluble  compounds  which  come  from  decaying  humus. 
In  order  to  have  plant  food  in  sufficient  quantity  in  or- 
dinary field  conditions,  it  is  necessary  to  have  humus  de- 
caying continuously.  If  the  humus  decays  too  rapidly, 
the  plants  cannot  use  all  of  it  and  part  will  be  wasted. 
If  the  humus  decays  too  slowly,  there  will  not  be  sufficient 
food  for  the  growing  plants  and  the  crop  will  be  small. 
Plants  may  be  grown  in  moist  sand  if  all  of  the  food 
elements  are  supplied,  but  this  is  a  difficult  process. 

Humus    serves   several    other    good  purposes    besides 


3i4  GENERAL  SCIENCE 

supplying  plant  food  when  it  decays.  It  increases  the 
capacity  of  soils  for  holding  water,  which  is  very  important 
in  sandy  soils  and  especially  during  dry  seasons  in  all  soils. 
The  decaying  humus  is  porous  and  acts  somewhat  like  a 
sponge  in  holding  water.  This  can  be  illustrated  by  taking 
equal  volumes  of  sandy  soil  and  soil  with  a  large  quantity 
of  leaf  mold  from  the  woods;  place  the  two  soils  under  the 
same  conditions,  moisten  them  thoroughly,  and  see  which 
will  hold  the  more  water  and  which  will  stay  moist  the 
longer.  (See  page  311.)  Humus  loosens  heavy  soil  and 
makes  it  possible  for  air  to  penetrate  more  deeply  and 
freely;  this  is  particularly  important  in  clay  soils,  as 
they  are  usually  heavy  and  compact.  It  furnishes  food 
for  bacteria  which  change  nitrogen  to  dilute  nitric  acid  so 
that  plants  can  use  it  for  food.  Decaying  humus  liber- 
ates carbon  dioxide  (carbonic  acid  gas)  which  acts  on  the 
minerals  of  the  soil  and  makes  them  soluble  for  the  use 
of  plants.  Humus  also  makes  it  more  favorable  for  those 
bacteria  to  live  which  take  free  nitrogen  from  the  air  and 
leave  it  in  the  soil  in  the  form  of  nitrates  which  can  be 
used  for  food  by  the  plants. 

A  moderate  amount  of  moisture  and  air  makes  the 
normal  condition  for  the  decay  of  humus  at  such  a  rate 
that  plants  will  receive  the  proper  supply  of  food.  If 
the  soil  is  too  well  aerated,  the  humus  will  decay  too 
rapidly.  If  the  soil  is  saturated  with  water,  most  of  the 
air  will  be  excluded;  then  the  decomposition  of  humus 
practically  ceases,  organic  matter  accumulates,  and  there 
is  no  plant  food  available.  Examples  of  this  can  be  found 
in  swamps  where  peat  and  muck  are  formed. 

Soils  that  receive  a  moderate  rainfall  have  about  four 
times  as  much  humus  as  soils  in  arid  regions.  But  the 
humus  in  soils  of  arid  regions  decays  much  more  rapidly 


THE   SOIL  315 

than  in  moist  soils,  and  it  also  contains  a  larger  per- 
centage of  nitrogen,  so  the  plants  receive  the  proper 
supply  of  food  in  either  case.  The  light  color  of  soils 
in  arid  regions  is  due  to  the  lack  of  humus  and  not  to  the 
lack  of  plant  food.  Dark  soils  sometimes  lack  one  or 
more  important  elements  of  plant  food.  This  must  be 
supplied  before  large  crops  can  be  grown. 

218.  Bacteria  and  "Other  Living  Organisms. —  Soil  is 
not  an  entirely  dead  substance.  It  is  much  more  than  a 
collection  of  rock  particles  containing  some  water.  It 
is  full  of  life,  and  without  this  life  the  valuable  grains 
and  vegetables  could  not  be  grown.  In  order  to  keep 
the  soil  productive  it  is  necessary  to  keep  the  helpful 
living  organisms  in  the  soil  healthy  and  well  supplied  with 
food.  Some  of  these  living  organisms  are  animals,  but 
most  of  them  are  the  lowest  forms  of  plants,  such  as 
molds,  and  the  one-celled  plants  such  as  bacteria  and 
yeast.  Some  bacteria  live  on  the  waste  products  of 
molds  and  other  bacteria,  and  thus  the  plant  food  is  worked 
over  and  over  until  it  finally  becomes  available  for  use 
in  proper  form.  If  there  is  not  enough  humus,  or  if  the 
humus  is  not  properly  decomposed  by  the  living  organ- 
isms, the  growing  plants  will  surfer  and  small  crops  will 
result. 

Molds  are  very  effective  in  breaking  down  woody 
organic  matter.  The  root-like  portions  of  the  mold 
soften  the  woody  tissue  of  plants  and  then  bacteria  can 
work  on  it  with  good  results.  The  effects  of  mold  can 
be  seen  by  keeping  some  old  bread  moist  for  a  few  days 
at  a  temperature  of  70°  to  90°  F. 

Earthworms  and  a  few  other  small  animals  help  to 
work  up  the  soil,  decompose  organic  matter,  and  keep 
the  soil  porous  by  making  holes  as  they  travel  through  it. 


3i6  GENERAL   SCIENCE 

Soil  full  of  earthworms  is  usually  fertile,  as  they  feed  on 
organic  matter.  The  most  important  of  all  living  organ- 
isms in  the  soil  are  the  bacteria  and  yeast  plants. 

Bacteria  are  so  small  that  they  have  to  be  magnified 
500  or  more  times  before  they  can  be  seen.  It  takes 
from  25,000  to  150,000  of  them  laid  side  by  side  to  make 
an  inch  in  length.  But  what  they  lack  in  size  they  make 
up  in  numbers  and  rapidity  of  reproduction.  If  they  have 
all  the  food  they  need,  and  if  the  other  conditions  are 
right,  there  will  be  a  new  generation  every  fifteen  to  thirty 
minutes.  They  increase  in  numbers  simply  by  one  bac- 
terium (singular  of  bacteria)  dividing  into  two  equal  parts, 
each  of  which  is  a  bacterium.  If  they  divide  every 
fifteen  minutes  there  will  be  four  generations  per  hour, 
and  at  the  end  of  the  hour  there  will  be  sixteen  new 
bacteria  from  each  bacterium.  If  enough  food  could  be 
secured,  the  offspring  of  one  bacterium  during  a  period  of 
four  or  five  days  would  be  sufficient  to  fill  all  the  oceans 
of  the  earth.  But  a  limited  supply  of  food  and  unfavor- 
able conditions  for  growth  prevent  this  rapid  increase  of 
bacteria  from  continuing. 

Bacteria  of  various  kinds  are  found  in  all  soils.  They 
range  from  less  than  30,000,000  per  ounce  up  to  billions 
per  ounce  of  soil.  The  most  fertile  soils,  like  those  in 
gardens,  contain  the  most  bacteria.  Some  experiments 
have  shown  that  the  soils  which  produce  the  greatest 
crops  contain  the  most  bacteria.  Some  soils  will  produce 
a  large  crop  of  one  kind  but  will  not  produce  a  crop  of  a 
different  kind.  This  is  sometimes  due  to  the  absence 
of  the  bacteria  that  a  certain  plant  needs.  Some  plants 
have  specialized  bacteria  and  will  not  grow  without  them. 
Alfalfa  is  such  a  plant,  and  if  it  does  not  grow  the  soil 
must  be  inoculated  with  alfalfa  bacteria  taken  from  the 


THE  SOIL 


317 


fields  where  alfalfa  has  been  growing.  Two  or  three 
bushels  of  soil  taken  from  an  alfalfa  field  and  scattered 
over  an  acre  of  ground  are  enough  to  inoculate  it  with 
alfalfa  bacteria.  Clover,  beans,  peas,  and  other  podded 
plants  have  a  special  kind  of 
bacteria  which  live  in  nod- 
ules on  their  roots.  These 
bacteria  in  the  nodules  can 
take  free  nitrogen  from  the 
soil  air  and  make  nitrates 
which  the  plants  can  use  for 
food. 

"The  different  chemical 
changes  produced  by  soil 
bacteria  are  quite  numerous. 
Some  kinds  are  specialized 
for  one  series  of  changes,  NQDUIES  C4TAINING  NlTROGES 
others  for  changes  of  a  dif-  Qn  the  roots  rf  a  Ieguminous  plant 
ferent  sort.  Some  will  at- 
tack by  preference  carbohydrates  like  starch  or  sugar, 
some  will  decompose  woody  tissue,  some  will  cause  the 
decay  of  proteins,  some  of  fats,  etc.  This  division  of  labor 
allows  an  effective  decomposition  of  humus.  Various 
gases  and  acids  are  produced  in  the  course  of  decay,  and 
help  to  decompose  the  rock  particles  in  the  soil  and  to 
render  the  mineral  plant  food  contained  in  them  available. 
The  insoluble  protein  compounds  in  the  roots  and  stubble 
are  broken  down  and  their  nitrogen  changed  partly  to 
ammonia.  The  particles  of  ammonia,  as  they  are  thus 
generated  by  bacteria  of  many  kinds,  are  at  once  pounced 
upon  by  a  special  class  of  germs  whose  function  it  is  to 
change  the  ammonia  into  nitrate.  Thanks,  therefore,  to 
the  activities  of  many  species  of  bacteria,  the  nitrogen 


3i8  GENERAL  SCIENCE 

locked  up  in  the  humus  and  in  green  manure  is  trans- 
formed gradually  into  nitrate,  and  is  then  quite  suitable 
for  the  building  of  roots,  stems,  leaves,  and  fruits." 
(From  Bulletin  of  the  U.  S.  Dept.  of  Agriculture.) 

Bacteria  are  one-celled  plants,  and  like  other  plants 
some  are  useful  and  others  are  harmful  and  cause  disease. 
There  are  more  than  1000  kinds  of  bacteria  and  only 
about  twenty  of  this  number  are  known  to  be  harmful 
to  man.  The  bacteria  which  cause  tuberculosis,  typhoid 
fever,  lockjaw,  and  diphtheria  are  called  disease  germs 
and  man  must  learn  to  keep  himself  healthy  or  these 
germs  will  decompose  his  body  and  death  will  result. 
Experiments  have  shown  that  certain  bacteria  in  food 
and  in  the  food-tube  of  animals  are  necessary  for  the 
existence  of  the  animals. 

219.  Chemical  Composition  of  the  Soil. —  All  the 
chemical  elements  of  which  plants  and  animals  are  com- 
posed are  found  in  the  soil;  most  of  them  are  in  the  dis- 
integrated rock,  and  the  others  compose  the  greater  part 
of  humus.  Humus  itself  contains  a  certain  amount  of 
the  elements  of  plant  food.  Elements  which  are  used  by 
nearly  all  plants  for  food  are  potassium,  sodium,  phos- 
phorus, sulphur,  magnesium,  silicon,  calcium,  iron,  chlo- 
rine, carbon,  hydrogen,  oxygen,  and  nitrogen,  and  a  very 
small  quantity  of  a  few  others.  These  elements  are  not 
taken  up  by  the  plants  in  pure  form.  They  are  combined 
into  numerous  compounds  and  these  compounds  must  be 
soluble  before  the  plants  can  use  them.  The  sulphates 
of  calcium,  magnesium,  sodium,  and  potassium  are  all 
soluble  in  water,  and  they  can  be  absorbed  by  the  roots 
of  plants.  The  nitrates  also  are  soluble  and  very  im- 
portant as  plant  food. 

When  humus  decays  most  of  the  carbon  escapes  into 


THE  SOIL  319 

the  air  in  the  form  of  carbon  dioxide,  and  thus  the  plants 
are  provided  with  a  means  of  taking  carbon  dioxide  from 
the  air,  breaking  it  up,  and  using  the  carbon  to  form 
compounds  for  building  material.  The  leaves  of  plants 
are  the  organs  which  manufacture  food  of  carbon  dioxide 
and  water.  A  large  part  of  the  body  of  plants  is  carbon. 
Of  the  elements  which  plants  take  from  the  soil,  nitrogen 
is  one  of  the  most  important;  it  is  also  the  most  diffi- 
cult to  keep  in  the  soil  and  the  most  expensive  of  all  plant 
foods  when  purchased  in  the  form  of  commercial  fertilizer. 

About  79  per  cent  of  the  air  is  nitrogen  —  an  inex- 
haustible supply  for  plants.  But  plants  growing  in  the 
air  would  starve  to  death  for  nitrogen  if  they  could  not  get 
it  from  the  soil  in  the  form  of  soluble  compounds.  Plants 
cannot  take  free  nitrogen  from  the  air.  This  being  true,  it 
is  necessary  that  farmers  learn  how  to  keep  a  supply  of 
nitrogen  in  the  soil.  The  nitrogen  compounds  in  the  soil 
decompose  readily  and  the  free  nitrogen  escapes  into  the 
air.  When  humus  decays  soluble  nitrates  are  formed, 
and  if  there  are  no  growing  plants  to  use  these  nitrates 
they  will  be  broken  up  and  the  nitrogen  will  escape. 
One  method  of  keeping  the  nitrogen  in  the  soil  is  to  keep 
a  crop  growing  during  the  time  when  humus  is  decaying, 
and  to  have  on  the  ground  in  winter  a  cover  crop  of  some 
kind  which  will  hold  the  nitrates  and  prevent  them  from 
being  leached  out  by  the  water.  These  cover  crops  can 
be  plowed  under  in  the  spring  and  will  then  form  humus. 

There  are  four  practical  ways  of  getting  nitrogen 
compounds  into  the  soil  when  they  are  deficient.  First, 
by  growing  weeds,  rye,  or  other  rapidly  growing  plants 
and  plowing  them  under  while  green  but  almost  mature. 
Second,  by  growing  clover,  cow  peas,  or  some  other 
legume.  If  several  crops  of  legumes  are  plowed  under, 


320  GENERAL  SCIENCE 

the  soil  will  be  well  supplied  with  nitrogen.  Third,  by 
covering  the  soil  with  manure  which  is  composed  of 
animal  excreta  and  waste  from  the  stems  of  plants,  and 
plowing  it  under.  Every  kind  of  decaying  organic  matter 
has  nitrogen  in  it.  Fourth,  by  buying  nitrates  in  the  form 
of  commercial  fertilizer  and  sowing  it  on  the  soil;  this 
is  usually  done  by  sowing  it  with  grain  seed  in  order 
that  it  may  help  to  produce  a  crop  without  much  waste. 
The  other  elements  of  plant  food  that  are  often  bought 
as  fertilizers  are  potassium  and  phosphorus.  Phos- 
phorus is  purchased  in  the  form  of  phosphoric  acid  and 
potassium  as  potash  or  muriate  of  potash.  Nitrogen  is 
sometimes  purchased  in  the  form  of  ammonia.  The 
nitrogen,  potassium,  and  phosphorus  compounds  are 
usually  mixed  in  known  proportions  and  sold  as  com- 
mercial fertilizer. 

QUESTIONS   AND  EXERCISES 

1.  Give  the  history  of  the  formation  of  the  soil. 

2.  Name  the  parts  of  good  soil. 

3.  How  does  the  weather  affect  rock  lying  on  the  surface? 
Does  rock  contain  food  for  plants?     Explain. 

4.  What  is  meant  by  soil  water?     How  can  it  be  retained  for 
plant  use? 

5.  How  much  of  the  soil  is  air  by  volume?    Prove  your  answer 
by  an  experiment. 

6.  Is  there  any  decaying  material  mixed  with  the  soil?     Of 
what  use  is  it? 

7.  Of  what  use  are  living  organisms  in  the  soil?     Could  plants 
grow  without  them?     Explain. 

8.  Which  plants  protect  soil  bacteria? 

9.  Which  method  of  keeping  the  soil  supplied  with  nitrogen 
is  the  cheapest?     Why? 


CHAPTER  XXXIII 
HOW  TO   CARE  FOR  SOIL 

220.  Value  of  this  Knowledge. —  Since  man  is  directly 
and  indirectly  dependent  upon  the  soil  for  his  food,  it  is 
important  that  he  should  learn  as  much  as  possible  con- 
cerning the  nature  of  soil  and  how  to  care  for  it  in  order 
that  he  may  be  able  to  keep  it  in  good  condition  for  the 
production  of  large  crops  with  the  least  amount  of  labor. 
The  animals  which  man  uses  for  food  live  upon  plants 
which  are  produced  by  the  soil;    this  is  the  indirect  de- 
pendence of  man  upon  the  soil  for  food.     The  production 
of   beautiful   flowers,    lawns,   and   trees   also   requires   a 
knowledge  of  the  soil.     In  order  to  grow  house  plants 
successfully  one  should  know  what  kind  of  soil  is  best 
for  them,  and  should  also  know  how  to  keep  the  soil 
in  flower  pots  in  good  condition.     Every  boy  and  girl 
should  know  how  to  care  for  plants  in  the  house,  or  in 
the  garden,  or  on  the  farm;   in  order  to  be  able  to  do 
this  it  is  necessary  to  know  something  of  the  nature  of 
soil  and  when  and  why  plants  are  cultivated. 

221.  When  to  Cultivate. —  There  are  three  principal 
types  of  soils,  namely,  clay  soil,  sandy  soil,  and  loam  soil. 
Clay  is  disintegrated  rock  almost  as  fine  as  flour.     Clay 
soil  holds  a  large  quantity  of  water  and  if  it  is  plowed 
while  wet,  during  clear  weather  the  sun  will  bake  it  and 
make  hard,  dry  clods.     Hence  it  should  never  be  plowed 
or  stirred  while  wet  enough  to  form  a  ball  when  squeezed 
in  the  hand.     Clay  soils  need  to  be  handled  with  greater 


322  GENERAL  SCIENCE 

care   than   any   other  kind,   especially  with  respect   to 
moisture  at  the  time  of  cultivation. 

Sandy  soil  is  composed  mostly  of  sand  through  which 
the  excess  water  soon  passes  by  nitration,  leaving  it 
dry  enough  to  be  plowed  in  a  short  time  after  a  rain. 
Sandy  soil  will  not  bake  or  pack  like  clay  soil  and  for 
this  reason  it  is  more  easily  cared  for,  although  it  is  best 
not  to  plow  it  when  too  wet. 

Loam  soil  is  composed  of  a  mixture  of  clay  and  sand. 
A  sandy  loam  has  a  large  per  cent  of  sand,  and  a  clay 
loam  has  more  clay  than  sand.  Loam  soils  are  the  best 
because  the  clay  in  them  prevents  the  water  from  escaping 
too  rapidly  and  the  sand  prevents  the  soil  from  packing 
and  from  being  baked  by  the  sun.  Loam  soils  can  be 
plowed  when  more  moist  and  when  dryer  than  clay  soils, 
but  it  is  best  not  to  plow  loam  soil  if  it  balls  when  squeezed 
in  the  hand. 

Soil  in  gardens,  flower  beds,  and  flower  pots  should  be 
stirred  when  it  is  moderately  moist  and  will  not  adhere 
to  a  great  extent  to  the  tool  being  used.  Plants  in  flower 
pots  will  do  better  if  the  soil  is  loosened  occasionally 
before  watering  them. 

222.  Why  Cultivate  Plants?  —  In  primitive  times  the 
soil  was  plowed  or  stirred  in  order  to  dispose  of  undesir- 
able vegetation  or  weeds  so  that  the  desired  crop  might 
not  be  hindered  in  its  growth.  Cultivation  for  this  one 
purpose  was  practiced  for  several  thousand  years  and  up 
to  very  recent  times.  Some  farmers  who  are  not  ac- 
quainted with  the  nature  of  the  soil  still  think  that  they 
cultivate  principally  to  destroy  weeds.  The  growth  of 
weeds  has  been  a  benefit  to  man  because  they  required 
the  crops  to  be  cultivated  and  thus  the  soil  was  made 
more  favorable  for  the  growth  of  the  desired  plants. 


HOW  TO  CARE  FOR  SOIL  323 

Under  modern  methods  of  progressive  farming  the  de- 
struction of  weeds  is  merely  a  secondary  matter,  while 
keeping  the  soil  in  a  favorable  condition  for  plant  growth 
is  the  principal  reason  for  cultivating  it.  Besides  the 
destruction  of  weeds,  the  following  are  the  chief  objects 
in  the  proper  cultivation  of  the  soil: 

(a)  To  loosen  the  soil  for  planting  seeds. 

(b)  To  remove  water  during  wet  seasons. 

(c)  To  retain  water  during  dry  seasons. 

(d)  To  get  air  into  the  soil. 

(e)  To  cause  the  decay  of  humus. 

Soils  are  plowed  and  pulverized  so  that  the  seeds  can 
be  planted  at  the  proper  depth  and  easily  covered.  It 
is  also  easy  for  the  young  plants  to  grow  to  the  surface 
and  for  the  roots  to  find  food  in  a  properly  prepared  soil, 
thus  giving  the  young  plant  favorable  conditions  for  rapid 
growth.  In  gardens  the  soil  is  prepared  for  the  seed  by 
use  of  the  spade,  the  hoe,  and  the  rake.  On  western 
farms  large  gang-plows,  followed  by  drags  and  harrows, 
are  drawn  by  steam  or  gas  traction  engines. 

While  the  crops  which  need  cultivation  are  growing, 
the  excess  water  during  a  wet  season  can  be  removed  by 
deep  cultivation,  because  this  permits  much  air  to  mix 
with  the  soil  and  also  exposes  the  lower  soil  to  the  open 
air,  allowing  a  large  amount  of  water  to  pass  off  by 
evaporation.  Care  must  also  be  taken  in  order  not  to 
cultivate  when  the  soil  is  too  wet,  or  both  the  crop  and 
the  soil  will  be  injured. 

During  dry  seasons  the  water  can  be  kept  from  evapo- 
rating from  the  soil  by  very  shallow  cultivation.  Several 
shallow  cultivations  during  a  dry  season  make  dust  of 
the  surface  of  the  soil.  This  dust  prevents  the  water 
from  escaping  by  evaporation.  During  dry  seasons 


324  GENERAL  SCIENCE 

water  comes  to  the  surface  from  several  feet  below  and 
this  water  is  usually  sufficient  to  grow  a  good  crop  if  it 
is  not  permitted  to  escape  by  evaporation.  In  gardens 
during  dry  seasons  the  surface  should  be  raked  lightly 
just  after  each  little  shower,  so  that  the  surface  will  not 
crack.  Soil  which  is  not  pulverized  on  the  surface  and 
is  permitted  to  crack  will  dry  out  very  quickly. 

About  one-half  the  volume  of  ordinary  soil  is  air.  This 
is  called  soil  air,  and  it  is  very  necessary  for  growing  plants. 
Cultivation  keeps  the  soil  loose  and  makes  room  for  air, 
which  occupies  all  the  spaces  between  the  little  lumps  or 
particles  of  soil.  Soil  that  is  very  wet  does  not  have 
much  room  for  air  and  most  plants  do  not  grow  well  in  it. 
As  excess  water  is  removed  air  enters. 

Good  soils  contain  a  small  percentage  of  decaying  plant 
matter  and  some  animal  matter.  This  plant  and  animal 
matter  is  called  humus.  It  is  decomposed  and  made  soluble 
by  the  action  of  microscopic  bodies  called  bacteria  and 
also  by  small  animals  living  in  the  soil.  These  bacteria 
and  small  animals  cannot  live  in  the  soil  if  there  is  too 
much  water  or  if  there  is  not  enough  water  in  it.  They 
also  need  air.  Proper  cultivation  is  necessary  to  make 
conditions  favorable  for  the  growth  of  these  organisms  in 
order  to  make  food  available  for  the  growing  plants. 

223.  Soil  in  Flower  Beds,  Pots,  and  Hotbeds.—  The 
soil  for  flower  beds  should  be  enriched  with  a  well-bal- 
anced commercial  fertilizer  and  some  manure  or  with 
a  large  quantity  of  well-decayed  manure.  This  manure 
should  be  thoroughly  mixed  with  the  rest  of  the  soil. 
The  soil  should  be  cultivated  often  enough  to  keep  it 
loose  and  well  aired  or  aerated.  During  dry  seasons 
sufficient  water  should  be  added  to  keep  it  moist  but 
not  wet. 


HOW  TO  CARE  FOR  SOIL  325 

The  soil  in  flowerpots  should  be  about  the  same  as  in 
flower  beds.  The  pot  should  have  a  hole  in  the  bottom 
to  drain  off  the  excess  water.  The  soil  should  be  kept 
moist  by  applying  a  little  water  daily.  If  the  soil  is  too 
dry,  the  leaves  of  the  plant  will  wilt ;  if  the  soil  is  too  wet, 
the  leaves  will  turn  yellow.  The  soil  in  the  pot  should 
be  loosened  occasionally  by  digging  it  up  with  a  stick. 
Do  not  use  a  sharp  tool  or  the  roots  will  be  cut. 

Hotbeds  are  made  by  digging  a  hole  about  sixteen 
inches  deep  and  as  large  as  desired.  Put  about  twelve 
inches  of  manure  in  the  bottom  and  then  cover  this  with 
soil  from  four  to  six  inches  deep.  The  heat  generated 
by  the  decaying  manure  warms  the  soil  so  that  the  seeds 
planted  in  it  start  to  grow.  The  soil  should  be  protected 
from  the  cold  air  by  a  box  or  board  construction  with  a 
window  sash  for  a  cover.  This  glass  cover  is  used  to 
let  in  light  and  heat  from  the  sun  when  it  is  shining.  The 
heat  from  the  manure  and  from  the  sun  shining  through 
the  glass  cover  will  raise  the  temperature  of  the  soil  so 
that  the  plants  will  grow  rapidly. 

224.  Soil  Drainage. —  In  hilly  sections  care  must  be 
taken  to  prevent  the  water  from  draining  away  too  rapidly, 
or  else  the  soil  will  be  carried  with  it  and  in  a  short  time 
what  is  left  will  become  unproductive  and  unfit  for  use. 
By  keeping  the  soil  well  supplied  with  humus  and  by 
keeping  it  covered  with  vegetation,  the  water  from  rains 
may  be  made  to  flow  off  very  slowly;  most  of  it  will  filter 
into  the  soil  and  then  flow  away  as  underground  water. 

In  rolling  districts  the  slopes  are  just  about  steep 
enough  to  carry  away  the  excess  water  slowly,  and 
usually  no  damage  is  done.  It  is  not  difficult  to  keep 
the  soil  on  gentle  slopes  supplied  with  humus  and  vegeta- 
tion and  thus  prevent  surface  erosion.  Tiles  placed  in 


326  GENERAL  SCIENCE 

the  ravines  will  aid  in  carrying  away  surface  water  without 
damage  to  the  soil. 

In  low  lands  where  the  slope  is  not  sufficient  to  carry 
off  the  excess  water,  the  farmers  have  to  resort  to  artificial 
drainage.  Some  dig  ditches  every  few  rods,  but  these  are 
a  hindrance  to  extensive  and  free  cultivation.  The  best 
method  is  to  lay  tile  eighteen  to  twenty-four  inches  below 
the  surface.  The  tile  drains  will  carry  away  the  excess 


AN  IRRIGATED  ALFALFA  FIELD 

water  and  permit  the  air  to  enter  the  soil  more  freely 
and  thus  the  soil  will  become  more  favorable  for  the 
growth  of  plants. 

Much  water  is  removed  from  wet  soil  by  evaporation, 
but  this  keeps  the  soil  too  cold  for  rapid  plant  growth, 
because  a  large  amount  of  heat  is  required  to  make  the 
water  evaporate.  For  this  reason  wet  soils  stay  cold 
longer  in  the  spring  than  soils  which  are  well  drained 
of  their  excess  water. 

225.  Irrigation. —  In  regions  where  the  rainfall  is  not 
sufficient  for  farm  crops  to  grow,  the  farmers  use  arti- 
ficial means  of  moistening  the  soil  if  sufficient  water  can 
be  obtained  at  reasonable  cost.  Dams  are  built  in  moun- 


HOW  TO   CARE  FOR  SOIL 


327 


tain  streams  to  hold  back  the  water  during  wet  seasons 
or  when  the  snow  on  the  mountains  melts.  This  con- 
trolled water  is  usually  permitted  to  flow  through  canals 
to  the  farming  lands. 
Each  farmer  has  one 
or  more  small  canals 
running  through  his 
farm  and  branch 
canals  to  his  various 
fields.  From  the 
smallest  canals  the 
water  is  permitted 
to  flow  out  between 
the  rows  of  trees  or 
rows  of  crops  that 
may  be  growing. 
The  water  is  con- 
trolled by  opening 
and  closing  flood- 
gates of  the  branch 
canals.  Water  is 
sometimes  allowed 
to  flow  over  the  soil 
when  the  crops  need 
it.  Since  the  crops  can  be  given  water  at  the  time  when 
it  is  needed,  larger  crops  can  be  grown  than  in  many 
unirrigated  districts  where  the  crops  have  to  depend  upon 
rain  for  water.  For  this  reason  it  is  a  good  investment 
to  spend  money  for  irrigation.  Even  in  the  middle  states 
some  progressive  farmers  have  a  system  of  watering  their 
vegetables  and  small  fruits  during  long  dry  periods. 
Berries  while  getting  ripe  need  a  great  amount  of  water, 
and  often  the  crop  can  be  doubled  by  having  a  small  irri- 


IRRIGATION  PROJECTS  OF  THE  U.  S. 
GOVERNMENT 

Sites  of  dams  and  reservoirs. 


328 


GENERAL  SCIENCE 


gation  system  to  supply  water  when  the  needed  rain  does 
not  come.  Gardeners  near  cities  use  the  city  water  and 
sprinkling  hose  to  supply  extra  water. 

The  United  States  Reclamation  Service  under  the 
Department  of  the  Interior  has  reclaimed  large  sections 
of  the  desert  land  of  the  West  by  building  dams  in  streams 
to  hold  the  water  so  that  it  can  be  diverted  from  its 


AN  IRRIGATION  CANAL  IN  ARIZONA 

natural  course  to  fertile  fields  where  large  crops  are  now 
being  grown.  The  farmers  pay  from  $30  to  $60  per  acre 
for  their  "water  right." 

The  Roosevelt  dam  in  Salt  River,  Arizona,  is  280  feet 
high  and  1080  feet  long.  It  forms  a  lake  of  25.5  square 
miles  and  will  irrigate  190,000  acres  of  land.  The  Sho- 
shone  dam,  Wyoming,  is  328  feet  high,  108  feet  thick 
at  the  bottom,  and  only  200  feet  long  at  the  top.  This 
is  the  highest  dam  in  the  world.  The  reservoir  created 
by  it  has  an  area  of  6,600  acres  and  a  capacity  of  456,000 
acre  feet;  that  is,  it  will  hold  enough  water  to  cover  456,- 
ooo  acres  one  foot  in  depth.  Twelve  miles  below  this 


HOW  TO    CARE   FOR   SOIL  329 

dam  is  the  low  diversion  dam  which  turns  the  water 
through  a  tunnel  3^  miles  long  into  the  main  canal, 
which  can  supply  water  for  164,122  acres  of  land. 

The  crops  grown  on  the  Shoshone  lands  are  alfalfa,  hay, 
wheat,  oats,  barley,  potatoes,  sugar  beets,  fruits,  and 
green  vegetables.  Dairying  and  bee  culture  are  also 
increasing,  the  products  having  a  high  market  value. 

226.  Effect  of  Sun's  Heat  on  the  Soil.—  The  sun  warms 
the  soil  so  that  it  is  possible  for  plants  to  grow;   it  also 
causes  excess  water  to  evaporate.     While  this  evaporation 
is  taking  place  rapidly,  the  soil  is  not  warmed  very  much. 
If  the  soil  is  not  properly  cared  for,  the  sun's  heat  will 
evaporate  the  water  that  should  be  retained  for  the  crops. 

If  the  soil  that  has  a  high  per  cent  of  clay,  or  is  all  clay, 
is  plowed  while  wet,  instead  of  moist,  the  sunshine  will 
dry  it  so  quickly  on  the  surface  that  it  will  become  very 
hard,  and  it  is  then  very  difficult  to  pulverize  it,  and  it 
also  often  loses  much  of  its  fertility.  Sandy  soil,  or  soil 
with  a  large  amount  of  humus  in  it,  will  not  be  easily 
baked  by  hot  sunshine. 

Clay  soil,  if  it  is  not  stirred  on  the  surface  after  a  rain, 
will  dry  hard  and  crack.  These  cracks,  running  in  all 
directions  over  the  surface,  permit  the  soil  water  to 
evaporate  rapidly  and  in  a  few  days  the  crop  will  be 
suffering  because  of  insufficient  water.  Clay  soils  should 
be  stirred  on  the  surface  as  soon  as  dry  enough  after  each 
rain  and  the  water  will  be  held  for  the  use  of  the  crop. 

227.  Erosion. —  Erosion  is  a  wearing  away  of  the  land 
by  the  wind  and  water.     You  have  seen  clouds  of  dust 
in  the  streets  of  cities  and  on  country  roads  or  even  in 
dry  fields.     This  dust  may  not  appear  to  amount  to  very 
much,  but  tons  of  solid  matter  are  moved  from  place 
to  place  by  strong  winds,  even  in  climates  of  moderate 


330  GENERAL  SCIENCE 

rainfall.  In  places  like  western  Kansas,  where  strong 
winds  are  usually  blowing,  much  soil  is  moved  by  the 
winds  just  after  the  farmers  have  plowed  their  fields. 
Sometimes  the  soil  particles  and  sand  are  flying  in  the 
wind  in  such  quantity  that  clouds  of  dust  can  be  seen 
from  great  distances.  Along  some  of  our  seashores  and 
lake  shores,  small  hills  of  sand  are  made  by  the  wind. 
These  sandhills,  called  dunes,  do  not  stay  in  one  place, 


EROSION  IN  A  NEGLECTED  FIELD 
On  a  very  gentle  slope. 

but  move  slowly  in  the  direction  of  the  prevailing  winds. 
The  sand  is  picked  up  on  the  windward  side  of  the  dune 
and  then  falls  on  the  leeward  side  where  the  wind  is  less 
strong.  On  the  shores  of  Lake  Michigan  these  sand 
dunes  move  slowly  eastward  and  sometimes  bury  valu- 
able farm  lands  or  even  forest  trees.  The  farmers  try 
to  prevent  the  movement  of  the  dunes  by  planting  shrub- 
bery and  making  fences  on  the  windward  side  so  that 
the  wind  cannot  pick  up  the  sand  and  carry  it  to  the 
opposite  side. 

In  most  parts  of  the  United  States  the  erosion  caused 


HOW   TO    CARE   FOR   SOIL  331 

by  water  is  much  more  noticeable  than  the  erosion  caused 
by  wind.  You  can  notice  evidence  of  erosion  during 
every  summer  shower.  Water  flowing  on  the  street,  or 
in  ravines  in  the  country,  is  made  muddy  by  the  small 
particles  of  solid  matter  that  it  is  carrying.  Ditches  of 
various  sizes  on  slopes  and  hillsides  and  the  ravines 
through  which  the  water  runs  were  made  by  the  flowing 
water  and  are  evidence  of  rapid  erosion.  Most  valleys 
are  results  of  water  erosion.  The  hills  usually  contain 
rock  that  is  not  easily  decomposed  and  carried  away  by 
the  water;  for  this  reason  they  have  remained  longer 
than  the  earth  that  was  carried  away  between  them, 
but  they,  too,  are  slowly  being  carried  away. 

Water  flowing  in  creeks  and  rivers,  carrying  sand, 
gravel,  and  at  times  stones  that  weigh  hundreds  of  pounds, 
grinds  the  rocks  in  the  beds  of  the  streams  into  finer  and 
finer  particles,  and  also  digs  into  the  banks  on  either  side. 
The  water  cutting  into  the  banks  of  the  stream  causes  it 
to  widen  its  course  and  to  flow  back  and  forth  across  its 
valley;  but  a  valley  is  not  made  until  the  bed  of  the 
stream  is  cut  down  to  a  comparatively  low  level.  Make 
a  careful  examination  of  ditches  on  the  hills  or  in  the 
fields.  Notice  the  influence  of  vegetation,  such  as  grass, 
crops,  or  trees,  on  erosion.  Observe  the  work  done  by 
creeks  or  rivers,  and  also  the  shape  and  width  of  the 
valleys. 

Erosion  caused  by  the  waves  beating  against  the  shores 
of  lakes  and  oceans  is  also  very  evident.  The  wind  some- 
times causes  the  water  to  form  waves  several  feet  high, 
and  these  waves  beat  against  the  shores  and  rocky  cliffs, 
sometimes  with  tons  of  force,  and  the  rocks  lying  at  the 
base  of  a  cliff  are  gradually  ground  to  sand  and  carried 
out  into  deeper  water. 


332  GENERAL  SCIENCE 

The  large  quantity  of  earth  moved  by  the  process  of 
erosion  is  not  destroyed,  but  is  deposited  in  various 
places  for  a  time.  The  dust  moved  by  the  wind  may  fall 
anywhere.  The  fertile  valley  of  a  river  is  made  of  the 
soil  carried  from  the  hills  and  mountains.  The  slow 
moving  water  of  a  river  is  unable  to  carry  with  it  the 
quantity  of  soil  brought  to  it  by  its  various  tributaries. 
This  solid  matter  is  spread  over  the  flood  plain  during 
each  flood,  and  thus  some  of  the  richest  farming  land 
is  made.  Every  river  valley  serves  as  an  example  of 
this  rich  soil  deposited  by  rivers. 

The  very  fine  particles  of  solid  matter  are  carried  into 
lakes  and  oceans  by  rivers,  and  at  the  river's  mouth  they 
settle  to  the  bottom  or  are  carried  far  out  by  strong 
currents  which  pass  the  river's  mouth.  Deltas,  such  as 
those  of  the  Mississippi  and  the  Nile,  were  formed  by  the 
deposits  of  solid  matter  which  the  river  carried  to  its 
mouth. 

It  can  easily  be  seen  that  the  hills  and  mountains  are 
slowly  but  surely  being  worn  away  and  carried  into  low 
lands  and  finally  into  the  oceans.  Some  geologists  say 
that  the  whole  Mississippi  basin  is  being  carried  to  the 
Gulf  of  Mexico  at  the  rate  of  one  foot  in  5000  years. 

228.  How  to  Protect  Soil  against  Erosion. —  We  must 
not  think  of  erosion  as  entirely  harmful.  The  disinte- 
grated rock  of  the  soil  contains  some  elements  and  com- 
pounds which  are  of  no  value  to  plants  as  food.  Very 
slow  and  gradual  erosion  removes  much  of  this  undesir- 
able waste  material  so  that  the  roots  of  plants  can  get 
to  new  rock  and  find  food. 

When  erosion  goes  on  very  rapidly  much  of  the  soil 
which  contains  plant  food  is  carried  away;  this  form  of 
erosion  is  undesirable  and  should  be  prevented.  The 


HOW   TO   CARE   FOR   SOIL  333 

method  is  very  simple.  It  can  be  done  by  keeping  the 
soil  well  supplied  with  humus  and  by  keeping  the  surface 
covered  with  vegetation,  especially  during  the  seasons 
of  the  year  when  erosion  goes  on  most  rapidly.  Large 
quantities  of  humus  or  decaying  material  absorb  much 
water  during  showers  and  also  keeps  the  soil  loose  so  that 
excess  water  will  sink  and  be  drained  off  as  underground 


A  CREEK  BED 
Filled  with  gravel  and  stone  too  heavy  for  the  water  to  carry. 

water  instead  of  on  the  surface.  Vegetation  holds  the 
water  on  the  soil  till  it  sinks  in,  and  also  prevents  the 
formation  of  small  streams.  Moreover,  it  keeps  the  soil 
full  of  roots  so  that  what  little  water  runs  off  the  surface 
cannot  carry  much  soil  with  it.  Crops  like  corn  which 
need  to  be  cultivated  several  times  should  not  be  grown 
on  the  same  land  many  times  in  succession  because  con- 
tinuous cultivation  causes  the  humus  to  decay  rapidly  and 
these  crops  do  not  leave  many  roots  in  the  ground  to 
prevent  erosion;  hence  a  cultivated  crop  should  be  fol- 
lowed by  a  non-cultivated  crop  or  several  non-cultivated 


334  GENERAL  SCIENCE 

crops,  like  wheat,  grass,  or  clover.  Slopes  and  hillsides 
need  more  care  to  prevent  erosion  than  low  lands,  and 
many  farmers  have  ruined  much  of  their  land  by  not 
guarding  against  erosion. 

QUESTIONS  AND   EXERCISES 

1.  Why  is  it  important  to  know  how  to  care  for  soil? 

2.  What  is  the  effect  if  soil  is  cultivated  while  very  wet?     If 
very  dry?  ; 

3.  What  kind  of  soil  is  in  your  community?     Does  it  dry  out 
quickly?     Why?     What  could  be  done  to  improve  it? 

4.  Why  do  you  cultivate  the  soil?     How  can  moisture  be 
retained  in  soil? 

5.  What  kind  of  soil  do  you  have  in  your  flowerpots  and 
flower  beds?     How  should  it  be  cared  for? 

6.  What  is  being  done  to  reclaim  the  desert  lands  of  western 
United  States? 

7.  What  can  be  done  to  keep  rains  from  washing  away  the 
surface  soil?     Is  it  a  benefit  or  injury  to  have  some  of  the  soil 
washed  away?     Why? 

8.  How  does  sunlight  affect  soil?     Is  it  better  to  have  soil 
bare  or  covered  with  vegetation?     Why? 


CHAPTER  XXXIV 
HOW  PLANTS   GROW 

229. —  In  order  to  be  able  best  to  care  for  plants  in 
the  home,  in  the  garden,  or  on  the  farm,  it  is  necessary 
to  know  a  few  things  in  detail  concerning  seeds,  roots, 
stems,  leaves,  flowers,  and  fruits.  If  we  know  something 
of  the  structure  and  uses  of  each  part  of  a  plant  and  the 
conditions  under  which  each  part  can  thrive  best,  we  shall 
be  more  successful  in  growing  plants.  To  know  the  use 
of  each  part  will  also  enable  us  to 
protect  it  from  its  enemies,  such 
as  insects  and  parasitic  diseases. 

230.  Seeds. —  Place  a  few  beans 
(large  beans  will  be  best)  in  water 
for  about  twenty-four  hours  or  in 
warm  water  for  a  few  hours  and  KIDNEY  BEANS 

then  examine  them  carefully.    The     One  is  sPlit:  °Pen  to  show 

.     .  r  the  embryo  plant. 

outer    covering,    consisting    of    a 

leather-like  membrane,  can  easily  be  removed.  After  this 
covering  is  taken  off  the  bean  divides  easily  into  two 
equal  parts;  each  half  is  a  seed  leaf.  At  the  end  of  one 
of  the  halves  is  a  very  small  bean  plant,  with  root,  stem, 
and  leaves.  Two  leaves  are  plainly  visible;  when  the 
beans  are  planted  the  longer  part  of  the  young  plant  grows 
down  into  the  ground  and  forms  the  roots.  When  this 
tiny  bean  plant  starts  to  grow  it  needs  food.  This  food 
is  in  the  two  halves  of  the  bean.  Beans  are  food  for  man 
and  also  for  the  young  plant  in  each  bean,  when  it  grows. 


336  GENERAL  SCIENCE 

The  bean  contains  chemical  ferments  which,  under  the  in- 
fluence of  warmth  and  moisture,  digest  the  stored  food  and 
make  it  soluble  for  the  growing  plant.  We  observed  that 
the  two  halves  are  connected  to  the  tiny  plant  at  one  end. 
Through  this  connection  the  digested  food  flows  as  the 
growing  bean  plant  needs  it. 

If  we  examine  soaked  peas,  pumpkin  seeds,  cucumber 
seeds,  flax  seeds,  apple  seeds,  peach  seeds,  etc.,  we  shall 
find  that  they  have  parts  corresponding  to  the  parts 
of  the  bean.  All  of  these  plants  and  many  more  have 
two  seed  leaves.  All  of  our  forest  trees  except  the  ever- 
greens produce  seeds  with  two  seed  leaves. 

231.  Grain. —  Corn,  wheat,  oats,  rye,  and  a  few  others 
are  called  grains  and  are  quite  different  in  structure  from 
the  bean.     Since  corn  grains  are  largest,  it  is  easier  to 
see  the  parts  in  them.     Soak  some  corn  for  about  twenty- 
four  hours  or  in  warm  water  for  a  few  hours  and  then 
find  the  parts  that  correspond  to  the  parts  of  the  bean. 
The  leathery  covering  can  be  removed,  but  not  so  easily 
as  from  the  bean.     The  hollow  or  sunken  side  of  the 
grain  contains  the  seed  leaf,  and  in  the  middle  of  this 
leaf  we  find  the  tiny  corn  plant.     The  end  of  this  plant 
toward  the  cob  end  of  the  grain  is  the  root  and  the  other 
end  forms  the  top,  when  it  grows.     We  see  that  the  seed 
leaf,  and  there  is  only  one,  and  the  young  plant  form  but 
a  small  part  of  the  entire  grain.     The  larger  part  of  the 
grain  contains  food  for  the  little  plant,  and  the  seed  leaf 
also  has  some  food  in  it. 

232.  How  to  Test  Seeds  and  Grains  for  Nutrients.— 
Take   a   little   corn   starch  and  mix  it  with  water,  add 
a  drop  or  two  of  a  weak  solution  of  iodine  and  observe 
the  color.     Now  put  a  few  drops  of  the  iodine  solution 
on  soaked  beans  and  corn  and  see  if  the  color  shown  by 


HOW   PLANTS    GROW  337 

the  starch  appears;  if  so,  then  beans  and  corn  contain 
starch.  Split  some  corn  grains  both  ways  and  see  which 
part  of  the  corn  is  mostly  starch. 

To  test  for  protein,  take  some  white  of  an  egg  or  bread, 
which  we  already  know  contain  protein,  and  put  on  it 
some  strong  nitric  acid  and  observe  the  yellow  color; 
then  add  a  few  drops  of  ammonia  and  notice  the  yellow 
color  change  to  orange.  Save  a  sample  of  the  yellow 
and  orange  colors  for  comparison  with  other  tests.  Now 
put  strong  nitric  acid  on  some  beans  and  corn,  giving  it 
several  minutes  to  act;  observe  the  color  and  then  add 
some  ammonia.  Do  corn  and  beans  contain  protein? 

By  holding  a  corn  grain  to  the  light  we  can  see  a  small 
section  on  either  side  through  which  light  seems  to  pass; 
this  part  contains  oil  or  fat. 

233.  Germination. —  When  the  young  plant  in  a  seed 
or  grain  starts  to  grow,  we  call  that  germination.  In 
order  to  make  sure  that  we  learn  how  it  takes  place,  it 
will  be  best  to  plant  seeds  of  various  kinds.  Plant  them 
about  one  inch  deep  in  moist  soil,  sand,  or  sawdust,  or 
between  moist  blotting  paper;  remove  one  or  two  each 
day  and  examine  them  carefully  to  see  how  they  are 
growing  and  which  parts  are  growing.  Plant  some  beans, 
peas,  pumpkin  seeds,  corn,  and  wheat,  and  note  carefully 
the  difference  in  the  way  they  come  out  of  the  soil.  What 
is  the  difference  between  the  growth  of  beans  and  peas? 
Between  pumpkins  and  beans?  Between  corn  and  beans? 
Does  the  root  or  the  top  start  from  the  seed  first?  Why? 

All  kinds  of  seeds  and  grains  contain  digestive  ferments 
called  enzymes.  An  enzyme  in  grains  is  called  diastase. 
Diastase  is  a  chemical  ferment  which  changes  starch  to 
sugar  without  itself  being  changed.  When  the  plant  starts 
to  grow  more  diastase  is  produced  from  the  grain.  Plants 


338  GENERAL  SCIENCE 

can  use  only  soluble  foods,  and  since  starch  is  but  very 
slightly  soluble,  it  is  changed  to  sugar  —  which  is  easily 
soluble  —  for  the  use  of  the  plant. 

The  conditions  necessary  for  these  enzymes  to  act 
are  also  the  conditions  necessary  for  rapid  germination. 
What  is  the  temperature  of  the  air  in  the  room  where 
plants  are  growing?  What  is  the  temperature  of  the  air 
outside  when  seeds  are  planted?  By  experimenting  we 
shall  find  that  a  temperature  near  75°  F.,  or  24°  C.,  is 
favorable  for  the  germination  of  seeds.  A  moderate 
amount  of  moisture,  or  enough  to  keep  the  seeds  damp, 
is  best.  The  seeds  of  the  most  useful  plants  will  not 
germinate  if  they  are  covered  with  water  or  if  the  soil 
is  kept  too  wet.  The  reason  for  this  is  that  germinating 
seeds  need  air,  and  they  cannot  get  sufficient  air  while 
covered  with  water.  Place  some  beans  and  corn  in  water 
for  several  days  and  see  if  they  will  grow.  The  conditions 
necessary  for  germination  are  a  moderate  temperature, 
a  moderate  amount  of  moisture,  and  air  or  oxygen,  as 
they  use  only  the  oxygen  of  the  air.  We  can  easily  prove 
that  light  is  not  necessary  for  germination  by  giving 
some  seeds  the  three  necessary  conditions  and  then 
wrapping  them  in  black  paper  to  exclude  the  light. 

234.  Roots. —  We  recall  that  we  saw  in  beans  and  corn 
the  part  of  the  young  plant  which  during  germination 
becomes  the  first  true  root  of  the  plant,  and  that  we 
observed  that  the  root  grows  first  during  germination. 
The  root  grows  into  the  soil  to  get  water  and  soluble  food 
for  the  stem  and  top  of  the  plant.  Roots  take  water 
and  food  from  the  soil  before  all  the  food  in  the  seed  or 
grain  is  consumed.  The  way  in  which  roots  take  up  soil 
water  is  an  interesting  process  and  to  learn  how  it  is  done 
we  shall  have  to  perform  some  simple  experiments. 


HOW   PLANTS    GROW 


339 


Also  showing  air  spaces. 
Magnified. 


If  we  place  some  mustard,  radish,  or  turnip  seeds 
between  moist  blotting  paper  and  keep  the  paper  moist 
for  two  or  three  days,  we  shall  find  that  the  roots  of  the 
germinating  seeds  are  covered  with  tiny  white  threads, 
standing  straight  out  from  the  root, 
and  some  of  them  about  an  eighth 
of  an  inch  long.  These  white  threads 
are  called  root  hairs,  and  they  take 
up  most  of  the  moisture  for  the  grow- 
ing plant.  Root  hairs  are  composed 

of  only  one  cell,  and  the  soil  water  RoOT  HAms  IN  THE  SOIL 
flows  into  them  and  thence  into 
the  main  root.  All  new  roots  are 
covered  with  these  root  hairs.  When  large  trees  start  to 
grow  in  the  spring,  they  first  grow  very  small  new  roots  at 
the  ends  of  the  old  ones  and  these  new  roots  are  covered 
with  root  hairs  which  absorb  the  soil  water  for  the  trees. 
These  root  hairs  are  composed  of  protoplasm  and  are 
filled  with  sap  which  is  more  dense  than  ordinary  soil 
water;  the  soil  water  passes  through  the  thin 
wall  of  the  root  hair  and  then  into  the  larger 
root.  This  process  by  which  a  liquid  flows 
through  an  animal  or  plant  membrane  is 
called  osmosis,  and  the  greater  flow  is  toward 
the  denser  liquid.  The  pressure  caused  by 
osmosis  in  the  roots  is  sufficient  to  lift  the 
sap  many  feet. 

If  no  osmosis  apparatus  is  at  hand,  the 
effect  of  osmosis  can  be  shown  in  the  follow- 
ing way:  Fasten  a  glass  tube  to  the  narrow  end  of  an  egg 
with  paraffin  or  sealing  wax;  then  with  a  long  wire  care- 
fully puncture  the  shell  of  the  egg  inside  of  the  glass  tube 
so  that  the  contents  of  the  egg  can  flow  up  the  tube. 


ROOT  HAIRS 
ON  A  YOUNG 
ROOT 


340  GENERAL  SCIENCE 

Carefully  remove  some  of  the  outer  shell  from  the  larger 
end  of  the  egg,  but  do  not  injure  the  tough  membrane 
just  inside  the  shell  or  the  contents  of  the  egg  will  flow 
out.  Now  fasten  the  egg  so  that  the  larger  end  is  in  water 
and  the  glass  tube  standing  vertically.  After  a  few  hours 
the  white  of  the  egg  will  be  forced  up  the  tube  by  the 
water  flowing  through  the  membrane  at  the  bottom,  the 
greater  flow  being  toward  the  denser  liquid. 

The  general  direction  of  roots  is  downward;  but,  like 
the  tops  of  plants,  they  send  out  branches  which  grow 
sideways  and  sometimes  just  beneath  the  surface  of  the 
soil.  These  branch  roots  send  out  other  branches  which 
may  grow  either  up  or  down  or  sideways.  They  will  not 
grow  up  out  of  the  soil,  but  they  grow  close  to  the  surface 
where  they  can  get  abundant  dissolved  food.  Many  roots 
of  corn  run  horizontally  close  to  the  surface.  There 
are  three  things  which  determine  or  influence  the  direction 
in  which  roots  grow:  (i)  Force  of  gravity  tends  to  cause 
roots  to  grow  downward.  (2)  Roots  grow  most  rapidly 
where  there  is  abundant  food,  because  they  receive  more 
nourishment.  (3)  Water  influences  the  direction  of 
growth.  If  the  soil  is  dry,  the  deeper  roots  will  grow 
because  they  have  a  food  supply.  If  the  soil  is  excessively 
wet,  the  surface  roots  will  grow,  and  the  deeper  roots  will 
turn  upward  or  to  a  horizontal  position  to  keep  out  of 
the  water;  for  this  reason  the  soil  should  be  well  drained 
to  permit  the  roots  to  go  deeper  and  thus  have  a  larger 
feeding  area  and  also  sufficient  water  when  a  dry  season 
comes.  If  the  roots  are  all  near  the  surface,  plants  suffer 
for  want  of  water  during  a  dry  season. 

235.  Stem. —  Recall  the  part  of  the  young  plant  in 
the  seeds  and  grains  which,  during  germination,  grew  and 
formed  the  stem  or  the  part  of  a  plant  above  the  ground. 


HOW   PLANTS    GROW 


34i 


We  also  observed  that  the  general  direction  of  growth 
of  the  stem  is  upward,  opposite  to  that  of  the  first  roots. 
The  stem  takes  a  vertical  position,  that  is,  vertical  to 
the  horizontal  plane.  The  trees  on  a  hillside  do  not  stand 
perpendicular  to  the  slope,  but  perpendicular  to  the  hori- 
zontal plane  of  the  earth.  The  branches  from  the  main 
stem  grow  outward  as  do  root  branches.  The 
roots  grow  outward  to  get  food,  while  the 
branches  from  the  stems  grow  outward  to  get 
light. 

If  we  examine  the  structure  of  a  cornstalk 
and  a  limb  of  a  tree,  we  notice  a  marked  dif- 
ference. The  cornstalk  has  a  hard  rind  and 
a  large  pith  with  hard,  stiff  fibers  running 
through  it.  There  is  no  true  bark  like  that 
on  a  tree  or  like  that  on  flax.  The  micro- 
scope shows  that  these  threads  in  the  pith 
and  also  in  the  rind  of  the  cornstalk  are  full 
of  holes  running  lengthwise,  through  which 
the  sap  flows. 

The  cross-section  of  the  limb  of  a  tree  contains  a  very 
small  pith  in  the  center  and  a  true  bark  on  the  outer 
edge  and  hard  wood  between  the  pith  and  bark.  We 
can  see  distinct  rings  in  the  woody  part;  these  are  the 
annual  rings  and  the  space  between  any  two  rings  is  the 
wood  that  grew  during  one  summer.  There  are  also  lines 
or  rays  running  out  from  the  center  to  the  bark,  much 
like  the  spokes  of  a  wheel.  These  lines  all  extend  to  the 
bark,  but  they  do  not  all  extend  to  the  pith  because  a 
few  of  the  rays  are  started  in  each  annual  ring  and  are 
continued  after  they  are  once  started.  These  rays  serve  as 
storehouses  for  food  and  for  the  flow  of  sap  across  the  tree. 

If  we  examine  with  a  magnifying  glass  the  smoothly 


SPLIT  STEM  OF 
A  TREE 

p,  pith;  h, 
hard  wood;  s, 
sap  wood;  b, 
bark. 


342  GENERAL  SCIENCE 

cut  end  of  a  tree  limb  or  the  end  of  a  piece  of  board,  we 
shall  find  it  full  of  very  small  holes.  The  soil  water 
taken  in  by  the  root  hairs  passes  up  through  these  holes. 
These  holes  or  tubes  are  not  usually  more  than  a  few 
inches  long.  The  ends  are  separated  from  one  another 
by  a  very  thin  partition  or  membrane  through  which  the 
sap  passes  by  osmosis.  By  osmosis  the  sap  continues 
to  pass  from  tube  to  tube  until  it  reaches  the  leaves  at 
the  ends  of  the  limbs  or  the  top  of  the  tree.  By  examin- 
ing the  cross-section  of  a  large  tree  like  the  oak,  we  find 
a  white  ring  an  inch  or  more  in  thickness  just  inside  the 
bark.  This  white  wood  is  living  and  is  called  sap  wood; 
most  of  the  sap  flows  up  through  this  living  part.  The 
brown  wood  inside  the  white  ring  is  dead  and  is  useful  for 
food  storage  and  to  support  the  tree.  This  brown  part 
is  most  valuable  for  lumber  because  it  does  not  decay  so 
quickly  as  the  sap  wood.  All  first-class  lumber  has  the 
sap  wood  removed. 

The  bark  of  a  tree  is  dead  on  the  outside  and  is  con- 
tinually falling  off;  much  of  it  may  be  pulled  or  cut 
from  many  kinds  of  trees  without  injury  to  the  tree. 
The  dead  part  of  the  bark  on  a  young  tree  or  twig  is 
very  thin  and  should  not  be  removed.  This  outer  bark 
serves  to  protect  the  tree  from  insects  and  diseases. 
The  inner  part  of  the  bark  next  to  the  sap  wood  is  living 
and  is  called  cambium,  or  the  cambium  layer.  This  cam- 
bium layer  forms  bark  on  its  outer  side  and  new  wood 
on  the  inner  side  next  to  the  sap  wood.  It  makes  this 
wood  and  bark  out  of  the  digested  food  which  flows  down 
from  the  leaves  through  the  cambium  and  the  bark  next 
to  it. 

The  outer  bark  of  some  trees  is  very  useful  to  man. 
The  bark  of  oaks  and  of  hemlock  is  used  for  tanning 


HOW   PLANTS    GROW  343 

leather.  The  cork-oak  has  a  very  thick  outer  bark  which 
is  somewhat  spongy  but  water-proof  and  is  valuable  for 
corks  for  bottles.  It  is  taken  from  the  trees  in  large 
sheets  and  the  corks  are  often  cut  perpendicular  to  the 
flat  surface. 

236.  Leaves. —  We  again  recall  that  beans,  squash 
seeds,  peas,  etc.,  have  two  seed  leaves,  and  that  there 
are  two  very  small  leaves  visible  on  the  young  plant  in 
the  beans.  These  two  little  leaves  become  the  first  true 
leaves  of  the  bean  after  it  germinates.  We  have  noticed 
that  all  the  plants  which  we  have  grown  formed  leaves  as 
soon  as  they  came  through  the  soil.  This  being  true, 
we  conclude  that  leaves  are  useful  and  necessary  to  plants. 
To  determine  whether  they  are  useful,  from  day  to  day 
pick  leaves  from  a  few  young  plants,  and  see  how  it 
affects  their  growth. 

Gather  a  dozen  or  more  leaves  of  various  plants  and 
compare  them  to  see  in  what  respects  they  are  the  same. 
Do  they  all  have  a  stem?  This  stem  is  called  the  petiole. 
The  broad  body  of  the  leaf  is  called  the  blade.  In  the 
blade  there  are  lines  or  ridges  called  veins.  The  sap  flows 
through  these  veins.  When  these  veins  branch  and  run 
in  all  directions,  the  leaf  is  said  to  be  netted-veined. 
Oak,  bean,  maple,  etc.  have  leaves  that  are  netted- 
veined.  When  the  veins  all  run  in  the  same  direction 
the  leaf  is  parallel- veined.  Corn  and  many  grasses  have 
parallel-veined  leaves.  In  general,  seeds  that  have  two 
seed  leaves  produce  plants  with  netted-veined  leaves  and 
grains  with  one  seed  leaf  produce  plants  with  parallel- 
veined  leaves. 

Most  leaves  are  covered  with  very  fine  hairs  or  a  whitish, 
woolly  substance,  usually  more  on  the  under  surface  than 
on  top.  This  extra  covering  helps  to  keep  water  out  of 


344 


GENERAL   SCIENCE 


SECTION  OF  A  LEAF 

e,  epidermis;  c, 
cells  containing 
chlorophyll  bodies; 
p,  intercellular  pas- 
sages; g,g,guard  cells, 
of  stoma.  Magnified. 


the  leaf  during  a  wet  season  or  during  rain;  it  may 
also  help  to  keep  out  disease  bacteria  and  parasitic 
plants.  If  we  dip  a  green  leaf  in  water,  we  can  see  that 
a  thin  layer  of  air  is  held  on  the  leaf  by 
this  extra  covering,  and  when  the  leaf 
is  removed  from  the  water,  the  water 
does  not  adhere  to  the  surface  of  the  leaf. 
The  blade  of  the  leaf  has  a  thin  layer 
of  cells  forming  the  upper  and  lower 
covering  or  skin  of  the  leaf;  this  layer 
is  called  the  epidermis.  Just  under  the 
upper  epidermis  is  a  layer  of  long  cells 
with  their  ends  against  the  epidermis 
and  arranged  in  column  form ;  hence  the 
layer  which  they  form  is  called  the  pali- 
sade layer.  Between  this  palisade  layer 
and  the  lower  epidermis  is  a  layer  of  loosely  arranged  cells 
with  large  air  spaces  between  them ;  this  layer  is  the  spongy 
tissue.  The  air  in  these  air  spaces  in  the  spongy  tissue 
can  pass  in  and  out  through  very  small 
openings,  which  are  in  the  lower  epi- 
dermis of  most  leaves.  These  open- 
ings in  the  lower  epidermis  are  called 
stomata  (plural  of  stoma).  There  may 
be  many  thousand  stomata  to  each 
square  inch  of  surface.  The  air  passes 
in  and  out  of  the  stomata  by  filtration. 
There  are  two  almost  semicircular  cells  ^  ordinary  epider_ 
around  each  stoma,  which  can  easily  be  malcell;  g,  guard  cell. 

.  ,  .  .1  n    j     Magnified. 

seen  with  a  microscope ;   they  are  called 
guard  cells.     By  changing  their  shape  they  control  the 
amount  of  air  that  can  pass  through  and  also  control  the 
amount  of  evaporation  of  water  from  the  leaf. 


LOWER  SURFACE  OF 

LEAF 


HOW   PLANTS   GROW  345 

The  roots  of  a  plant  take  up  soil  water  by  osmosis 
and  it  flows  up  through  the  stem,  through  the  petiole  of 
the  leaf,  and  through  the  veins  into  the  palisade  layer. 
The  air  is  composed  of  about  .04  per  cent  of  carbon  di- 
oxide (CO2).  This  carbon  dioxide  passes  through  the 
stomata  into  the  leaf,  where  it  and  the  soil  water  are 
used  as  the  raw  materials  for  the  manufacture  of  starch. 
The  energy  necessary  for  this  manufacturing  process 
comes  from  the  sun  in  the  form  of  heat  and  light.  Rapid 
starch  making  by  leaves  requires  a  moderate  temperature 
and  abundant  sunlight.  Each  cell  of  the  leaf  between 
the  lower  and  upper  epidermis  is  full  of  green-colored 
bodies  called  chlorophyll  bodies.  These  give  the  green 
color  to  the  entire  leaf.  The  chlorophyll  bodies  are 
formed  in  the  leaf  when  it  is  exposed  to  sunlight.  When 
a  leaf  is  shaded,  the  chlorophyll  disappears  and  the  leaf 
turns  white  or  yellow.  This  can  be  seen  by  lifting  a 
board  that  has  lain  for  some  time  on  grass,  by  growing 
some  plants  in  the  dark,  or  by  noticing  the  yellow  leaves 
on  the  under  part  of  a  tree  that  produces  a  dense  shade. 

These  chlorophyll  bodies  in  the  presence  of  sunlight 
make  starch  by  combining  water  (H20)  with  carbon 
dioxide  (C02):  6C02  +  sH20  =  C6Hi005  +  i2<3. 

This  starch,  made  during  the  day,  must  be  changed 
to  sugar,  a  soluble  substance,  before  it  can  be  moved 
from  the  leaf  down  the  stem  of  the  plant,  where  it  is 
stored  in  the  form  of  starch  (the  sugar  having  been  changed 
back  to  starch),  or  it  is  joined  with  other  elements  in  the 
soil  water  and  then  used  for  growth,  or  it  is  stored  in 
ripening  fruits  in  the  form  of  protein,  or  the  sugar  may 
be  changed  to  fat  or  oils  and  stored  in  the  fruit.  Name 
some  fruits  or  seeds  that  contain  starch,  or  proteins,  or 
oils.  What  commercial  oils  come  from  fruits  or  seeds? 


346  GENERAL  SCIENCE 

We  now  see  why  plants  and  trees  should  be  thinned  out 
sufficiently  to  permit  them  to  get  air  and  sunlight. 
Plants  that  are  crowding  one  another  cannot  be  healthy 
and  productive.  Fruit  trees  that  are  not  properly  pruned 
and  thinned  have  so  many  branches  that  they  cannot  all 
get  sunlight  and  sufficient  air,  and  so  the  lower  and  inner 
fruit-spurs  or  branches  die  and  what  little  fruit  is  grown 
is  of  inferior  quality.  Fruits  like  peaches  and  apples  are 
covered  with  openings  for  the  inward  and  outward  pas- 
sage of  gases,  and  for  this  reason  they  need  sunlight  and 
air  or  they  will  not  grow  properly  and  will  not  be  colored. 
Even  small  twigs  are  covered  with  openings  for  the  pas- 
sage of  gases;  these  openings  can  be  seen  with  the  unaided 
eye  and  are  called  lenticels. 

Man  and  other  animals  are  dependent  upon  the  leaves 
of  plants  for  their  food  either  directly  or  indirectly. 
Hence  man  must  learn  how  to  care  for  the  plants  that 
he  wishes  to  cultivate  in  order  to  make  them  productive. 

237.  Flowers. —  When  a  seed  germinates,  it  first  grows 
a  root,  then  stem,  leaves,  and  finally  at  a  comparatively 
mature  stage  flowers  appear.  The  flower  is  grown  for 
the  purpose  of  producing  new  plants.  To  find  how  this 
is  done  it  is  necessary  to  make  a  close  study  of  complete 
flowers.  Examine  some  flowers  of  fruit  trees,  or  wild 
flowers  from  the  woods,  or  some  in  the  home,  and  find 
all  the  parts.  We  shall  see  that  some  flowers  contain 
parts  which  are  not  necessary  for  reproduction  and 
some  which  are  necessary  for  reproduction;  the  former 
we  call  non-essential  parts  and  the  latter  essential  parts. 

The  non-essential  parts  consist  of  the  calyx  and  corolla. 
The  calyx  is  the  outer  whorl  of  leaf-like  parts  of  the 
flower  and  is  often  green  in  color.  One  of  the  divisions 
of  the  calyx  is  called  a  sepal.  The  corolla  is  the  second 


HOW   PLANTS    GROW  347 

whorl  of  leaf-like  parts  just  inside  the  calyx.  The  parts 
of  the  corolla  are  called  petals  and  they  are  usually 
colored. 

These  parts  which  are  non-essential  for  reproduction 
are  the  parts  which  give  beauty  to  blossoms  and  which 
make  flowers  so  attractive  for  decorative  purposes,  and 
also  give  them  their  high  commercial  value.  Florists 
aim  to  grow  principally  those  plants  which  produce 
beautiful  sepals  and  petals;  so  from 
the  standpoint  of  the  florist  the  non- 
essential  parts  are  very  desirable. 

The  essential  parts  consist  of  sta- 
mens and  pistil.  The  stamens  are  usu- 
ally within  the  corolla,  and  each  stamen 
is  composed  of  (i)  a  thread-like  part 
called  the  filament,  (2)  the  anther,  FLOWER 

which  is  often  a  knob-like  body  on 
the  outer  end  of  the  filament,  and  (3)  the  pollen,  which 
is  usually  a  yellow,  powdery  substance  that  grows  in 
the  anther.  The  pollen  dust  is  composed  of  two-celled 
bodies  of  various  shapes,  which  may  be  plainly  seen  when 
viewed  through  a  microscope.  The  stamens  are  the  male 
parts  of  a  flower. 

The  pistil  is  in  the  center  of  a  flower  and  is  composed 
of  three  parts.  The  base  of  it  is  called  the  ovary,  which 
is  usually  the  largest  part  of  the  pistil  and  contains  little 
bodies  called  ovules;  these  can  often  be  seen  with  the 
unaided  eye.  On  top  of  the  ovary  is  a  slender  stem 
called  the  style,  and  at  the  end  of  the  style  is  the  stigma. 
The  pistil  is  the  female  part  of  the  flower. 

For  fruit  to  be  produced,  the  pollen  from  the  anthers 
must  get  on  the  stigma.  It  does  this  in  several  ways. 
The  anthers  may  burst  when  they  are  ripe  and  throw 


348  GENERAL    SCIENCE 

the  pollen  on  the  stigma;  this  is  self-pollination.  Bees 
and  other  insects  may  carry  the  pollen  from  one  flower 
to  the  stigma  of  another  flower  of  the  same  kind;  this 
is  cross-pollination.  The  wind  may  blow  the  pollen  about 
and  some  may  fall  on  the  proper  stigmas.  Corn  is 
pollinated  by  the  wind. 

The  stigmas  are  covered  with  a  sweet,  sticky  sub- 
stance which  prevents  the  pollen  from  falling  off  and  also 
causes  the  pollen  grains  to  start  to  grow  or  germinate 
much  like  seed,  but  they  only  form  a  growth  corresponding 
to  the  first  root  of  a  germinating  seed.  The  pollen 
grain  forms  a  root-like  tube  without  branches,  which 
grows  down  through  the  stigma  and  style  and  into  the 
ovary.  In  the  ovary  are  ovules,  each  one  of  which  con- 
tains an  embryo  sac,  and  in  this  sac  is  an  egg  cell  which 
cannot  grow  unless  it  is  fertilized  by  the  sperm  cell  of  a 
pollen  grain.  This  sperm  cell  of  the  pollen  grain  goes 
down  the  pollen  tube,  and  when  the  pollen  tube  enters 
an  ovule  in  the  ovary,  the  sperm  cell  joins  with  the  egg 
cell  to  form  a  cell  known  as  a  fertilized  egg.  Each  pollen 
grain  can  fertilize  only  one  egg  cell,  so  each  pistil  needs 
as  many  pollen  grains  on  its  stigma  as  there  are  ovules 
in  the  ovary;  each  ovule  has  one  egg  cell.  In  order  to 
provide  for  this,  some  plants  grow  many  thousands  of 
pollen  grains  for  each  ovule  in  the  ovary.  In  the  case 
of  flowers  that  are  pollinated  by  the  wind  or  by  insects, 
much  of  the  pollen  goes  to  waste  and  never  falls  on  a 
stigma. 

After  the  egg  cell  is  fertilized,  it  immediately  starts  to 
grow  and  form  a  young  plant  with  root  and  top  like  that 
in  a  bean  or  in  a  grain  of  corn.  This  is  an  embryo  plant 
or  immature  plant.  While  the  embryo  plant  is  being 
formed,  the  parent  plant  stores  food  around  it.  When 


HOW   PLANTS    GROW  349 

the  embryo  is  of  sufficient  size  and  the  proper  amount 
of  food  is  stored,  the  ovary  is  mature  and  the  fruit  is 
ripe.  A  fruit  is  a  ripened  ovary. 

Fruits  and  seeds  are  scattered  by  the  wind,  water, 
animals,  and  by  the  fruit  pods  bursting  open  and  throwing 
out  the  seeds.  Fruits  are  grown  for  the  purpose  of  start- 
ing new  plants  away  from  the  parent  plants  and  also 
to  carry  plants  over  unfavorable  climatic  changes  like 
cold  weather  during  winter.  Man  makes  conditions 
favorable  for  plants  to  grow  so  that  they  will  produce 
large  quantities  of  fruit  for  food.  Make  a  list  of  plants 
grown  for  their  fruit;  keep  in  mind  that  a  fruit  is  a  ripened 
ovary. 

238.  Production  of  New  Varieties. —  In  the  previous 
section  we  learned  that  some  flowers  are  self-fertilized 
and  that  most  of  them  are  cross-fertilized  in  order  to 
produce  seeds  which  in  turn  produce  new  plants.  When 
the  pollen  from  a  flower  of  one  plant  falls  on  the  stigma 
of  a  similar  plant,  a  seed  is  grown  which  when  planted 
will  produce  a  plant  that  is  more  or  less  different  from 
either  of  the  two  parent  plants.  This  difference  may 
not  be  noticeable  or  it  may  be  very  great.  If  seed  is 
always  selected  from  plants  which  show  a  difference  from 
the  parent  plants,  new  varieties  may  gradually  be  pro- 
duced. This  selection  may  take  place  among  wild  plants 
and  thus  produce  new  varieties,  but  man  with  his  intelli- 
gence is  always  selecting  the  best  seed  from  the  most 
productive  plants  with  the  result  that  the  farm  crops 
per  acre. have  greatly  increased  and  many  new  and  pro- 
ductive varieties  have  been  produced.  Luther  Burbank 
of  California  has  produced  wonderful  results  simply  by 
selecting  the  plants  that  show  an  improvement  and  letting 
them  grow  to  produce  seed  for  the  next  crop.  Most 


350  GENERAL   SCIENCE 

farmers  can  still  greatly  improve  most  of  the  plants 
which  they  grow  by  selecting  seed  from  plants  which  show 
an  improvement  caused  by  cross-fertilization. 

Sometimes  cross-fertilization  produces  a  plant  that  is 
very  different  from  the  parent  plants.  When  these  far 
different  plants  can  be  made  to  reproduce  themselves, 
a  new  variety  comes  into  existence.  New  varieties  of 
corn,  wheat,  etc.  have  been  produced  in  this  way. 

239.  Seedless  Fruits. —  There  are  many  so-called  seed- 
less fruits,  such  as  navel  oranges,  lemons,  bananas,  and 
pineapples.  The  method  by  which  these  are  produced 
is  largely  one  of  selection  and  by  means  of  budding. 
Seedless  oranges,  lemons,  grapes,  and  bananas  bloom 
like  other  fruit  trees.  In  the  navel  oranges  the  embryo 
sac,  which  normally  would  develop  into  embryos  and  be 
fertilized  by  the  pollen,  disintegrates  before  fertilization 
takes  place;  hence  they  do  not  form  seeds,  but  the  fruit 
develops  as  usual  except  that  it  is  lacking  in  seeds. 
Occasionally  a  few  embryo  sacs  develop  normally,  and  in 
the  event  that  these  particular  embryo  sacs  happen  to 
become  fertilized  by  the  pollen  of  a  similar  variety,  there 
will  be  seeds  in  fruit  which  is  ordinarily  seedless.  For  this 
reason  seeds  are  occasionally  found  in  navel  oranges. 

When  a  tree  produces  nearly  all  seedless  oranges  or 
lemons,  it  is  propagated  by  budding  or  grafting,  that  is, 
a  bud  from  the  seedless  orange  tree  is  cut  off  and  fixed 
into  the  bark  of  a  young  orange  tree  in  such  a  way  that 
it  grows  and  forms  a  tree  that  produces  seedless  fruit 
like  the  one  from  which  the  bud  was  taken.  In  case  of 
grafting,  a  twig  is  taken  instead  of  a  bud.  In  this  way 
many  trees  are  soon  grown  from  which  buds  for  budding 
can  be  selected  from  the  trees  that  produce  the  most 
seedless  fruits.  The  young  orange  trees  which  are  budded 


HOW   PLANTS    GROW  351 

are  grown  by  planting  healthy  seeds  from  fruits  with 
seeds. 

In  the  case  of  the  banana,  however,  the  disintegration 
of  the  embryo  sacs  has  become  such  a  fixed  habit  that 
seeds  are  never  found  in  cultivated  varieties.  Pineapple 
plants  are  propagated  by  cuttings,  and  only  very  rarely 
can  a  seed  be  found  in  a  pineapple.  These  cuttings  are 
shoots  or  " suckers"  which  spring  up  from  the  base  of 
the  old  plants.  These  new  cuttings  bear  fruit  after  from 
fourteen  to  eighteen  months.  A  pineapple  plant  grown 
from  seed  does  not  grow  fruit  until  after  it  is  ten  or 
twelve  years  old. 

QUESTIONS   AND  EXERCISES 

1.  What  is  the  difference  between  beans  and  corn  on  the 
bases  of  appearance  and  structure? 

2.  What  nutrients  do  beans  and  cereal  grains  contain?     Why 
are  such  plants  grown? 

3.  Explain  the  process  of  germination  of  seeds. 

4.  What   are   the   necessary   conditions   for   the   growth   of 
healthy  plants  from  seeds? 

5.  In  what  direction  do  roots  grow?     Why?     Of  what  use 
are  roots  to  plants? 

6.  What  are  the  conditions  for  osmosis  to  take  place?     Does 
osmosis  occur  in  your  body? 

7.  Does  the  root  or  stem  grow  first  from  a  germinating  seed? 
What  are  the  parts  of  the  stem  of  a  plant?     Give  the  use  of 
each  part. 

8.  What  are  the  parts  of  a  leaf?     Give  the  use  of  each  part. 

9.  Is  it  better  for  trees  to  have  the  leaves  fall  off  every  year? 
Explain. 

10.  Why   do   plants  grow   flowers?     Name   the   parts  of  a 
flower.     Give  the  use  of  each  part. 

11.  How  are  new  varieties  of  plants  produced? 

12.  How  are  seedless  oranges  grown? 


CHAPTER  XXXV 
HOW   PLANTS   ARE   PROPAGATED 

240.  By  Use   of   Seeds.  —  Seeds   contain   an   embryo 
plant  with  sufficient  food  stored  with  it  to  support  it  till 
roots,  stem,  and  leaves  are  formed.     The  ground  must 
be  properly  prepared  so  that  the  roots  can  get  food  from 
the  soil  before  all  the  stored  food  of  the  seed  is  consumed. 

Corn  in  northern  United  States  is  usually  planted  in 
May,  in  rows  42  inches  apart  and  from  one  to  one  and 
one-half  inches  deep  in  the  soil.  Winter  wheat  is  sown 
in  September  and  October,  in  rows  eight  inches  apart 
and  about  one  inch  deep.  Small  seeds  like  clover  and 
many  garden  seeds  are  sown  on  the  surface.  The  surface 
of  the  prepared  soil  in  the  garden  is  usually  stirred  just 
enough  to  cover  the  fine  seeds.  Raindrops  cause  clover 
seed  to  settle  into  the  soil  enough  to  become  covered. 

241.  By  Use  of  Roots.  —  Many  cultivated  plants  are 
propagated  by  keeping  the  roots  over  the  winter  in  a 
place  where  they  will  not  freeze  and  then  planting  them  in 
the  spring.     Examples  are  dahlias  and  bulbs  of  tulips 
and  hyacinths.     In  the  North  sweet  potatoes  are  planted 
in  hotbeds  and  young  plants  grow  from  the  old  roots. 
These  plants  when  about  six  inches  high  are  transplanted 
about  10  inches  apart  in  rows  which  are  from  two  to  three 
feet  apart.     In  the  South  the  sweet  potatoes  are  cut  into 
small  pieces  and  planted  like  the  white  potatoes  in  the 
North. 


HOW  PLANTS   ARE   PROPAGATED 


353 


Many  garden  plants  are  propagated  by  both  roots  and 
seeds.  The  seed  of  onions  is  often  sown  so  thick  that  only 
small  onions  grow  the  first  season.  These  small  onions 
are  called  onion  sets,  and 
are  kept  over  the  winter 
and  planted  the  next  season 
to  produce  big  onions,  Cab- 
bages and  turnips  store  food 
the  first  year  in  the  head 
and  roots  respectively,  and 
will  grow  seed  the  second 
year  if  replanted. 

Many  wild  plants  repro-     SHOWING  PROPAGATION  OF  WHITE 
.  CLOVER  BY  RUNNING  STEM 

duce  by  seeds  and  roots  also. 

Nearly  all  of  the  early  spring  flowers  have  rootstocks  and 
bulbs  in  which  food  is  stored  for  early  growth.  The  May 

apple  spreads  by  growing  under- 
ground a  root  which  has  a  bud 
on  the  end  to  make  a  plant 
above  ground  the  next  season. 
Many  grasses  reproduce  by 
sending  out  stem-like  root- 
stocks  just  beneath  the  surface 
of  the  soil.  Blue  grass  is  an 
example. 

242.  By  Use  of  Cuttings.  — 
The  white  or  Irish  potato  is  a 
tuber  and  an  enlarged  under- 

GRAPE  CUTTING  AND  THE  SAME  ground  stem.  The  eyes  are  buds 
AFTER  ONE  YEAR'S  GROWTH  . 

which  will  grow  when  conditions 

are  favorable.  For  planting,  the  potatoes  are  cut  into 
pieces  with  two  or  more  eyes  on  each  piece.  One  or 
two  of  these  eyes  may  grow  and  produce  potato  stalks 


354 


GENERAL  SCIENCE 


which  in  turn  grow  new  tubers.     The  white  potato  grows 
wild  in  South  America. 

Many  plants  can  be  grown  by  cutting  a  branch  and 
placing  a  few  inches  of  the  larger  end  in  the  ground.  The 
branch  or  limb  must  have  buds  on  it.  The  part  which  is 
in  the  soil  will  grow  roots  and  that  part  above  the  soil 
will  grow  stem  and  leaves.  Examples  are  the  poplar, 
willow,  currant  bushes,  and  grapevines.  The  grape 
should  be  cut  with  three  buds  on  the  part  to  be  planted, 

two  buds  to  be  covered  with 
soil  and  the  third  one  left 
above  the  soil. 

243.  Grafting  and  Budding. 
-  Grafting  and  Budding  are 
forms  of  propagation  by  cut- 
tings and  are  used  for  the  pur- 
pose of  growing  fruit  of  the 
same  variety  as  that  from  which 
the  grafting  twig  or  bud  was 
taken.  Since  fruits  with  pulp, 
like  apples  and  peaches,  are  mostly  cross-fertilized  in 
the  blossom,  the  seeds,  if  planted,  will  not  produce  trees 
that  will  grow  fruit  just  like  the  parent  trees. 

The  most  important  thing  to  be  known  about  grafting 
and  budding  is  that  the  cambium  layer  of  the  bark  of  the 
two  parts  must  touch  in  such  a  way  that  the  sap  can  flow 
from  one  to  the  other.  For  grafting,  the  wedge-shaped 
cut  is  very  convenient  for  bringing  the  cambium  layer 
of  each  part  into  contact.  Twigs  about  six  inches  long 
may  be  cut  and  tapered  off  in  the  form  of  a  wedge  at  the 
end  opposite  the  terminal  bud.  The  grafting  twigs  are 
called  scions.  For  top-grafting  the  end  of  a  small  limb 
or  the  top  of  a  young  tree  is  cut  off  and  a  wedge-split 


GRAFTING  A  TOP  BRANCH 


HOW  PLANTS   ARE   PROPAGATED 


355 


made.  If  the  limb  is  larger  than  the  scions,  two  scions 
may  be  fixed  in  position  so  that  the  cambium  layers  touch 
properly,  and  then  covered  with  grafting  wax  and  wrapped. 
When  very  young  trees  are  grafted,  scions  of  the  same 
diameter  as  the  tree  are  used.  For  root  grafting,  small 


PROPAGATION  OF  PEACH  TREES 

1.  Peach  seed  selected  for  planting. 

2.  Bud  stick,  taken  from  the  tree  of  the  variety  wanted,  grown  on 
seedling  root. 

3.  Peach  bud  in  position. 

4.  Peach  seedlings,  one  season's  growth,  with  bud  placed  in  position, 
which  was  done  in  August  during  growth  of  seedling. 

5.  Peach  seedling  with  top  cut  off  above  the  bud,  in  the  spring  of  the 
year  following  after  the  bud  has  been  placed  in  position;   only  the  bud 
has  been  allowed  to  grow. 

6.  Peach  tree  dug,  showing  bud  top  and  seedling  root  six  months  after 
top  of  seedling  has  been  cut  off. 

7.  Peach  tree  showing  both  seedling  roots  and  bud,  trimmed  ready 
to  plant  in  orchard  or  permanent  place. 

roots  from  eight  to  twelve  inches  long  are  cut  and  scions 
of  the  same  diameter  are  placed  at  the  proper  ends, 
or  seedling  roots  may  be  used.  Root  grafting  is  now 
used  very  extensively  for  propagating  fruit  trees  of  known 
variety  and  quality. 

For  budding,  buds  instead  of  scions  are  cut  from  desir- 
able trees,  and  these  buds  are  set  in  proper  cuts  made  in 
very  young  trees.  Usually  a  T-shaped  cut  is  made  in  the 
bark  at  the  base  of  the  young  tree  and  the  bark  loosened 


356 


GENERAL  SCIENCE 


sufficiently  so  that  the  bud  can  be  put  in  position.  After 
the  bud  starts  to  grow  the  top  of  the  tree  is  cut  off  just 
above  the  bud.  Since  there  is  a  large  system  of  roots 
made  by  one  season's  growth  in  the  soil,  the  new  bud  will 


PROPAGATION  OF  APPLE  TREES 

1.  Seedling  one  year  old,  grown  from  seed 
trees  propagated  on  seedlings.     The  process  of 
budding  apple,  pear,  plum,  and  cherry  is  the 
same  as  the  peach  except  that  seedling,  instead 
of  seed,  is  planted  in  nursery  rows  and  the  bud 
is  usually  grown  two  years  instead  of  one. 

2.  Apple  scions  for  grafting  on  seedling  roots. 
Scions  are  taken  off  when  trees  are  dormant  in 
the  fall. 

3.  Splice  of  tongue  or  whip  graft. 

4.  Graft  and  root  united.     Bark  of  scions 
and  root  should  make  perfect  union.     Grafting 
is  usually  done  by  a  nurseryman  in  January 
and  February  and  placed  in  storage  for  spring 
planting. 

5.  A.   One  year  old  apple  from  graft,  show- 
ing growth  of  both  top  and  roots.     B.   Two 
year  old  apple  from  graft,  showing  two  years 
growth  of  top  and  roots. 

be  well  supplied  with  food,  hence  it  will  grow  rapidly. 
Budding  is  used  by  fruit  growers  more  extensively  than 
grafting. 

244.   Transplanting  —  Many    plants     can    be    grown 
on  a  very  small  area  while   they  are   young   or   mere 


HOW  PLANTS  ARE  PROPAGATED 


357 


seedlings,  and  can  be  cared  for  with  less  labor  and 
expense  than  if  the  seeds  were  planted  over  an  area 
required  for  mature  growth.  Seeds  of  cabbage  and 
tomato  and  lettuce  are  often  sown  in  hot  beds  and  when 
the  seedlings  are  from  four  to  six  inches  high,  they  are 
transplanted  where  each  plant  will  have  room  for  mature 
growth. 

All  kinds  of  fruit  trees  are  grown  by  planting  the  seeds 
a  few  inches  apart  in  rows  which  are  about  three  feet 
apart,  which  per- 
mits proper  cultiva- 
tion while  the  trees 
are  young.  The  sec- 
ond year  the  trees 
are  either  budded 
or  grafted  and  then 
they  are  allowed  to 
grow  from  one  to 
three  years  before 
they  are  trans- 
planted on  areas 
large  enough  for  them  to  grow  to  maturity  and  bear  fruit. 
Most  fruit  growers  now  plant  trees  which  have  tops  only 
one  year  old,  so  that  they  can  start  the  limbs  of  the  trees 
high  or  low  as  they  wish.  Trees  can  be  transplanted  in 
the  late  autumn  after  the  leaves  have  fallen,  or  in  the  early 
spring  before  the  buds  start  to  grow. 

For  transplanting  fruit  trees  or  shade  trees  successfully 
the  following  suggestions  may  be  followed: 
,   (a)  For  trees  with  a  top  one  year  old:    With  a  sharp 
knife  cut  all  branch  roots  back  to  about  one  inch  from  the 
main  or  primary  root. 

(b)  For  older  trees  leave  the  branch  roots  longer,  but 


SHOWING  How  TO  TRANSPLANT  AND  PRUNE 
YOUNG  TREES 


358 


GENERAL  SCIENCE 


be  sure  that  all  broken,  cracked,  or  bruised  roots  are  cut 
off  back  of  the  injury.  A  smooth  cut  will  heal  more 
quickly  than  a  break. 

(c)  Cut  the  top  back  in  the  same  proportion  that  the 
roots  have  been  cut.     A  transplanted  tree  with  a  large  top 
and  few  roots  will  die. 

(d)  Dig  the  hole  about  two  feet  square  and  15  to  20 

inches  deep.  Place  the  top 
soil  on  one  side  and  the  sub- 
soil on  the  other  side  of  the 
hole. 

(e)  Plant  the  trees  about 
one  inch  deeper  than  they 
were  before;  the  color  of  the 
bark  will  show  how  deep 
they  were  in  the  soil.  Put 
the  top  soil  into  the  bottom 
of  the  hole  and  around  the 
roots  and  tamp  it  solid 
with  your  feet  or  hands. 
Fill  the  hole  with  the  sub- 

LARGE  SUGAR  MAPLE  IN  A  FIELD     soil   and    tamP  again'      AP~ 

ply  water  if  the  soil  is  dry. 

(/)  If  planting  where  there  is  sod,  save  the  sod  to  be 
replaced;  but  leave  several  inches  of  space  between  the 
sod  and  the  tree. 

245.  Shade  Trees.  —  Shade  trees  around  country 
homes  and  on  the  streets  of  cities  serve  many  useful  pur- 
poses. They  add  beauty,  shield  the  houses  from  winds, 
and  in  summer  give  protection  from  the  sun's  heat  and 
also  serve  as  homes  for  birds;  on  these  accounts  shade 
trees  add  value  to  property. 

Those  trees  should  be  planted  which  are  easily  grown, 


HOW  PLANTS  ARE  PROPAGATED  359 

which  are  free  from  attacks  of  diseases  and  insects,  and 
which  produce  the  least  amount  of  objectionable  waste 
matter  (such  as  the  woolly  substance  on  the  leaves  of  the 
sycamore  or  buttonwood).  A  tree  on  which  the  leaves 
come  out  early  and  hang  till  late  autumn  is  also  desirable. 
The  particular  locality  will  determine  which  trees  possess 
these  characteristics. 

Trees  which  send  their  roots  into  sewers,  cisterns,  and 
wells  should  not  be  planted,  for  they  will  always  cause 
trouble.  The  poplar,  willow,  and  buttonwood  are  of 
this  type. 

246.  Forest  Trees.  —  The  American  people  have  been 
too  wasteful  and  careless  in  cutting  trees  and  are  now 
beginning  to  realize  the  loss  thus  incurred.  The  lumber- 
men are  being  advised  as  to  the  best  methods  of  caring  for 
the  young  trees.  The  waste  limbs  are  being  thrown  into 
heaps  to  prevent  the  spread  of  destructive  forest  fires. 
Young  trees  are  often  planted  where  old  trees  are  cut 
down,  so  that  the  forest  is  renewed.  Many  paper  mills 
own  the  forests  from  which  the  soft  wood  is  obtained  for 
making  paper  and  they  have  the  wood  cut  at  the  season 
when  the  most  new  sprouts  will  grow  from  the  stumps  of 
the  trees.  Then  in  10  to  20  years  they  can  cut  over  the 
same  ground  again.  Soft  wood  grows  rapidly. 

The  United  States  Department  of  Forestry  has  control 
of  thousands  of  acres  of  forest  land  and  trained  men,  called 
forest  rangers,  travel  about  in  these  forests  to  indicate 
what  trees  ought  to  be  cut  and  to  care  for  the  young  trees 
and  also  to  prevent  forest  fires. 

Every  farmer  or  large  landowner  ought  to  have  all 
waste  land  covered  with  trees,  if  possible.  Where  there 
is  no  waste  land  or  land  unfit  for  cultivation,  at  least  10 
per  cent  of  the  farm  should  be  growing  trees.  Pasture 


360  GENERAL  SCIENCE 

lands  should  have  trees  somewhere  for  the  protection  of 
the  stock  during  unfavorable  weather. 

QUESTIONS    AND    EXERCISES 

1.  At  what  time  of  the  year  are  the  various  crops  planted  in 
your  community? 

2.  Which  crops  are  grown  from  seeds?     Which  from  roots?     Which 
from  stems? 

3.  Cut  some  scions  and  graft  them  on  a  tree  of  the  same  kind. 
(Grafting  is  usually  done  in  the  spring  before  the  leaves  come  out.) 

4.  What  is  the  purpose  of  grafting  and  budding? 

5.  What  vegetables  and  trees  are  transplanted? 

6.  What  kinds  of  trees  are  best  for  shade?     How  should  they  be 
planted? 

7.  Are    there    sufficient    trees   in   your    community?    Are    they 
properly  cared  for? 


CHAPTER  XXXVI 
USE    OF   PLANTS   TO    MAN 

247.  Plants  for  Food.  —  Primitive  man  or  man  in  the 
savage  condition  gathered  much  of  his  food  from  wild 
plants,  using  the  roots  of  some  and  the  fruits  of  others, 
such  as  nuts  and  berries.  Later  he  learned  to  care  for 


HARVESTING  WHEAT  IN  WASHINGTON 

these  food-producing  plants  and  also  learned  to  cultivate 
productive  grasses  from  which  wheat,  rye,  oats,  and  rice 
were  developed.  The  latter  are  natives  of  Asia  and  have 
been  cultivated  by  man  for  several  thousand  years.  Corn 
originated  from  a  grass  which  is  a  native  of  Mexico.  The 


362 


GENERAL  SCIENCE 


American  Indians  cultivated  corn  with  their  crude  imple- 
ments. It  is  now  the  largest  food  crop  in  the  world  and 
more  corn  can  be  grown  per  acre  than  of  any  other  grain. 

Potatoes  are  natives  of  South  America.  They  were 
cultivated  by  the  Indians  and  were  not  used  by  white 
people  until  after  the  discovery  of  America.  Now  they 
form  a  large  part  of  man's  food. 


HARVESTING  SUGAR  CANE  IN  HAWAII 

Most  of  our  large  fruits  are  natives  of  Europe  and 
Asia.  With  modern  conveniences  of  transportation  and 
refrigeration  it  is  possible  for  people  in  temperate  climates 
to  get  tropical  fruits  in  large  quantity,  making  oranges 
and  bananas  as  cheap  as  apples.  Pineapple  culture  is 
increasing  rapidly  and  this  fruit  is  now  less  expensive. 

Modern  methods  of  canning  make  it  possible  to  preserve 
perishable  vegetables  and  fruits.  In  cans,  they  can  be 
transported  as  needed  and  will  not  spoil  if  they  are  kept 
at  medium  temperatures. 


USE  OF  PLANTS  TO  MAN 


363 


248.  Plants  for  Clothing.  —  Man  even  in  the  wild  or 
savage  state  must  have  food  in  order  to  live,  but  in  warm 
climates  he  can  do  without  clothing  and  so  he  wears  but 
very  little.  As  he  progresses  in  civilization  he  increases 
his  clothing  until  his  whole  body  is  covered.  Most  of  the 
primitive  clothing  was  made  of  skins  and  furs  of  animals, 


TRANSPLANTING  RICE  IN  JAPAN 

but  man  in  the  civilized  condition  has  learned  to  use  many 
kinds  of  plants  for  clothing.  Some  of  these  plants  are 
cultivated  and  some  grow  wild. 

Cotton  a  few  years  ago  was  cultivated  exclusively  for 
its  fine  fiber  which  was  and  is  used  for  making  clothing. 
Cotton  needs  a  long  season  for  its  growth  and  so  it  is 
raised  only  in  warm  climates.  In  the  southern  United 
States  it  is  usually  planted  in  March  and  harvested  in 
September  and  October.  The  seeds  are  covered  with  a 


364 


GENERAL  SCIENCE 


long  white  fiber  which  is  removed  from  the  seed  by  a 
machine  called  a  cotton  gin.  The  fiber  is  used  for  making 
thread,  yarns,  and  clothing.  The  oil  is  pressed  from  the 
seeds  and  is  known  as  cottonseed  oil.  It  is  used  for 
making  artificial  butter,  and  as  a  substitute  for  olive  oil, 
which  it  resembles. 


PICKING  COTTON  IN  ARKANSAS 

Flax  is  grown  in  temperate  climates.  The  northern 
United  States  and  Europe  produce  large  quantities.  It 
requires  a  great  deal  of  labor  to  care  for  it  properly.  Just 
before  the  seed  is  ripe  the  flax  stalks  are  pulled  up,  roots 
and  all,  and  kept  moist  during  a  period  of  "  retting,"  after 
which  the  inner  part  of  the  stem  and  the  outer  bark  are 
removed  from  the  sieve  cells  or  inner  bark.  This  inner 
bark  fiber  is  combed  into  very  fine  threads,  out  of  which 
linen  thread  and  clothing  are  made.  The  white  linens 


USE  OF  PLANTS  TO  MAN 


365 


have  been  put  through  a  long  bleaching  process  and  do 
not  wear  as  long  as  the  cream-colored,  unbleached  linens. 
Flax  is  also  grown  for  its  seed  from  which  an  oil  is 
extracted  and  used  for  making  paint.  This  oil  is  known 
on  the  market  as  "linseed  oil.''  The  inner  bark  of  the 
flax  cannot  be  used  to  make  linen  after  the  seed  is  ripe. 


HARVESTING  FLAX  IN  SOUTH  DAKOTA 

Hemp  and  sea  grass  are  used  for  making  rough  garments 
and  also  for  making  summer  hats  and  rugs.  The  straw 
of  wheat  is  used  extensively  for  making  hats.  The 
cellulose  or  wood  fiber  of  trees  is  used  for  making  arti- 
ficial silk.  The  cellulose  is  dissolved  and  then  forced 
through  very  fine  holes;  this  process  makes  a  fine,  lustrous 
fiber  that  can  be  made  into  clothing. 

Jute  is  an  East  Indian  plant  used  for  making  mats, 
rugs,  etc. 

249.  Plants  for  Ropes  and  Twines.  —  The  common  cord 
used  in  stores  is  made  of  cotton  fiber.  The  heavy  brown 


366  GENERAL  SCIENCE 

twines  are  made  of  flax,  hemp,  and  jute.  The  parts 
unfit  for  clothing  are  made  into  twines.  A  large  quantity 
of  small  rope,  the  size  of  wash  lines,  is  made  of  cotton. 
Binder  twine  and  large,  heavy  ropes  are  made  of  hard 
fiber  like  that  obtained  from  manila  hemp  and  sisal. 
Large  ropes  are  made  by  twisting  together  several  smaller 
ropes  or  twines. 

250.  Plants  for  Paper.  --  The  earliest  records  were  cut 
on  stones;   these  were  very  hard  to  handle  and  also  easily 
broken.     Later,  records  were  made  on  prepared  skins  of 
animals;   this  method  is  still  used  - —  examples  are  college 
diplomas.     Still  later,  the  fiber  of  the  papyrus  plant  which 
grows  in  Egypt  was  split  into  sheets  and  records  made 
on  it. 

After  printing  was  invented  it  became  necessary  to 
have  paper  in  large  amounts.  Parchment  made  of  skins 
of  animals  was  expensive  and  not  sufficient  in  quantity,  so 
paper  was  made  of  rags  (not  of  woolen  rags)  and  of  straw. 
But  as  the  great  printing  presses  came  into  use  these 
sources  of  paper  supply  were  not  sufficient.  Now  forest 
trees  are  cut,  ground  into  small  chips,  and  acted  on  by 
hot  chemicals;  the  wood  fiber,  cellulose,  is  then  thoroughly 
washed  and  rolled  into  large  sheets  of  paper.  The  paper 
of  this  book  is  made  of  wood.  Only  soft  wood,  like  the 
poplar  and  spruce,  is  used  for  paper  making. 

The  best  paper  is  made  of  linen  or  flax  fiber.  Cotton 
and  wood  make  a  paper  of  medium  quality.  Straw  makes 
very  poor  paper.  All  kinds  of  rags,  other  than  woolen, 
and  waste  paper  are  gathered,  baled,  and  sent  to  paper 
mills  to  be  worked  over  and  made  into  new  paper. 

251.  The  following  table  will  give  some  idea  of  the 
quantity  of  plants  produced  in  the  United  States  during 
the  year  1913. 


USE  OF   PLANTS  TO   MAN 


367 


Product 

Total  Acres 

Production 
per  Acre 
bu. 

Total  Yield 
Bushels 

Price  per 
Bushel 

Corn  

105,820,000 

23.1 

2,446,980,000 

69.1  cents 

Wheat  

50,184,000 

15.2 

763,380,000 

79-9 

Oats        

38,399,000 

29.2 

1,121,768,000 

39.2 

Barley  

7,499,000 

23.8 

178,189,000 

53-7 

Rve 

2,557,000 

16.2 

41,381,000 

63.4 

Buckwheat.  .  . 
Potatoes  

805,000 
3,668,000 

17.2 

90.4 

13,833,°°° 
331,525,000 

75-5 
68.7 

ANIMALS  REPORTED  FOR  1914 

Milk  cows 20,737,000    Value  per  head  $53.94 

Other  cattle  ..     35,855,°°°  3i-i3 

Swine 58,933,000      

Sheep 49,719,000      

Horses 20,962,000      

Silk  exported  from  Japan  during  the  year  1912 23,413,000  pounds 

QUESTIONS    AND    EXERCISES 

1.  What  is  the  historical  origin  of  the  principal  plants  used  for  food? 

2.  What   commercial   products   are   made   of   wheat,   rye,  oats, 
cotton,  potatoes,  and  flax? 

3.  Examine  various  kinds  of   rope  and   determine  the  kind   of 
material  of  which  each  is  made. 

4.  Make  a  list  of  the  plants  of  which  paper  is  made.    Which  ones 
have  you  seen? 


CHAPTER  XXXVII 
LOW   FORMS    OF   PLANT   LIFE 

252.  The  earth  is  covered  with  life,  much  of  which  to 
the   average   observer   consists  of   trees,   shrubs,   weeds, 
grasses,  and  cultivated  (useful)  plants.     But  these  plants 
which  are  most  visible  are  not  the  most  numerous.     The 
plants  with  green  leaves  are  able  to  take  food  from  the 
soil  and  air  and  to  make  the  three  nutrients  which  are 
used  for  growth  and  which  are  also  stored  in  the  seeds; 
such  plants  are  considered  to  be  high  in  the  scale  of  devel- 
opment or  evolution  and  they  serve  as  food  and  clothing 
for  man. 

Plants  which  do  not  have  distinguishable  leaves,  stem, 
and  roots,  we  consider  low  in  the  scale  of  development. 
Many  of  these  low  forms  of  plant  life  are  very  useful 
and  necessary  for  other  plants  and  for  man;  while  many 
of  them  are  harmful  to  both  higher  plants  and  animals. 
Some  of  them  are  useful  in  one  place  and  harmful  in 
another;  the  same  can  also  be  said  of  trees  and  grasses. 

These  low  plant  forms  are  divided  into  two  groups, 
namely,  Algae  and  Fungi. 

253.  Algae.  —  Algae  have  chlorophyll  and  are  able  to 
make  starch  of  water  and  carbon  dioxide,  thus  preparing 
their  own  food.     The  algae  vary  in  size  from  the  simple 
microscopic  form  to  the  largest  plant  in  the  world.     The 
giant  kelp  of  the  Pacific  Ocean  attains  a  length  of  over 
i?ooo  feet;    it  is  an  alga.     The  brown-colored  rockweed 


LOW  FORMS  OF  PLANT  LIFE 


369 


along  the  coast  is  an  alga.  Some  fresh-water  algae  are 
the  pond  scums,  which  can  be  found  on  the  water  in 
swamps  and  ponds.  Some  simple,  one-celled  algae  can 
be  found  on  rocks  and  on  the  bark  of  trees.  They  give 
to  the  rock  and  bark  a  greenish  color. 

One  pond  scum  is  known  as  spirogyra,  so-called  because 
of  its  spiral  appearance  under  the  microscope.  It  can  be 
found  floating  on  the  surface  of 
the  water  in  masses  composed  of 
hair-like  threads  with  bubbles 
of  gas  distributed  through  it. 
This  gas,  composed  mostly  of 
oxygen,  causes  the  spirogyra  to 
float.  It  grows  by  using  the 
impurities  in  the  water  and  the 
carbon  dioxide  of  the  air.  When 
starch  is  being  made,  there  is 
an  excess  of  oxygen  gas  which  is 
given  off  and  forms  the  bubbles 
which  hold  the  plant  on  the 
surface  where  it  can  get  more  sunlight  and  air.  This, 
plant  is  useful  in  so  far  as  it  lives  on  the  impurities  in 
the  water  and  gives  off  oxygen  to  the  air.  It  is  harmful 
to  the  extent  that  it  gets  into  drinking  water  and  gives 
it  a  peculiar  odor  and  taste. 

A  thread  of  spirogyra  is  made  up  of  a  single  row  of 
cells  attached  end  to  end.  A  thread  increases  in  length 
by  the  cells  dividing  —  one  cell  becoming  two  cells,  the 
ends  remaining  fixed  to  each  other. 

Spirogyra  does  not  bloom  and  grow  seed  like  the  higher 
plants,  but,  when  a  time  that  is  unfavorable  for  growth 
comes,  it  produces  a  cell  that  corresponds  to  a  seed.  This 
cell  is  known  as  a  spore,  sometimes  called  zygospore.  It 


SPIROGYRA  —  A  POND  SCUM 
A  is  one  cell;     B  is  two  spore 

cells  formed  by  the  union 

of  two  other  cells. 


370  GENERAL  SCIENCE 

is  formed  by  the  contents  of  two  cells  flowing  together 
to  make  one  strong  cell.  This  new  cell  can  withstand 
extreme  temperatures  and  also  dry  weather.  The  wind 
may  carry  it  about  as  dust,  and  when  it  falls  into  a  pond 
it  will  start  to  grow  and  form  a  new  plant  if  the  tempera- 
ture is  right.  These  spore  cells  are  usually  formed  by  the 
union  of  the  cells  of  two  threads  lying  side  by  side. 

254.  Fungi.  —  The  fungi  form  a  very  large  group  of 
plants  that  do  not  have  green  coloring  matter  or  chloro- 
phyll, and  so  cannot  make  starch  of  water  and  carbon 
dioxide.  Their  color  is  mostly  white,  and  they  live  on 
the  juices  of  other  plants  which  are  living  or  dead.  Those 
fungi  which  take  their  food  from  living  plants  are  called 
parasites,  and  are  generally  harmful.  Those  which  live 
on  decaying  matter  are  called  saprophytes,  and  most  of 
them  are  useful  except  when  they  grow  where  they  are 
not  wanted.  The  common  fungi  are  mushrooms,  molds, 
and  yeast. 

There  are  about  400  kinds  of  edible  mushrooms  which 
grow  wild  in  the  woods  and  fields.  Some  are  grown  under 
.cultivation.  The  part  of  the  mushroom  which  is  eaten 
is  only  the  spore-bearing  part.  The  roots  of  the  mushroom 
are  in  the  ground  or  in  decaying  matter  on  which  they 
grow.  One  mushroom  top  may  produce  millions  of 
spores  (seed-like  organs)  which  are  scattered  by  the  wind. 

The  molds  are  useful  in  decomposing  dead  matter  so 
that  it  can  be  used  again  by  higher  plants.  Molds  are 
harmful  when  they  decompose  useful  dead  matter  such 
as  lumber  and  foods.  One  common  kind  is  the  black 
mold  which  grows  on  bread.  To  grow  some,  take  a  piece 
of  old  bread,  moisten  it,  and  roll  it  on  the  floor  to  gather 
some  dust  containing  the  mold  spores,  and  then  put  it 
away  for  two  or  three  days,  being  sure  to  keep  it  moist. 


LOW  FORMS  OF  PLANT  LIFE  371 

The  mold  spores  on  the  bread  will  germinate  and  send 
their  root-like  threads  into  the  bread  to  absorb  the  food. 
In  a  day  or  two  these  threads  in  the  bread  will  be  large 
enough  to  send  up  above  the  surface  some  threads  with 
black  knobs  on  the  end.  Each  knob  is  full  of  ripe  spores 
waiting  to  be  carried  away  by  the  air. 

Yeasts  are  fungi,  and  there  are  many  kinds  of  them. 
They  are  harmful  when  they  grow 
on  fruits  and  in  fruit  juices  which 
we  want  to  keep  for  some  time. 
They  are  useful  for  producing  car- 
bon   dioxide    to    raise   bread,   and    YEAST  CELLS  WITH  BUDS 
for  fermenting    grains    and  other 
substances   for  the  production  of   commercial   alcohol. 

To  see  yeast  plants  with  the  microscope:  Mix  a  small 
piece  of  soft  commercial  yeast  in  a  little  water  containing 
a  small  amount  of  sugar,  let  it  stand  an  hour  or  so,  and 
then  take  a  drop  of  the  liquid  and  place  it  on  the  micro- 
scope slide.  The  oval-shaped  bodies  are  yeast. 

255.  Bacteria  compose  a  group  of  fungi  of  about 
1,000  kinds,  of  which  about  20  are  parasitic  to  man  and 
cause  disease;  the  others  are  useful  or  harmless.  These 
parasitic  bacteria  can  live  on  man  because  of  improper 
methods  of  living  on  the  part  of  most  people.  Man's 
uncleanness  and  over-indulgence  are  largely  responsible  for 
the  existence  of  parasitic  bacteria  which  produce  disease. 

Bacteria  are  useful  in  causing  the  decay  of  useless  dead 
matter,  which  can  then  be  used  by  growing  plants.  They 
are  absolutely  essential  in  the  soil  to  produce  foods  for 
various  plants.  Most  plants  have  to  have  their  particular 
kind  of  bacteria  in  the  soil  or  they  cannot  grow.  Bacteria 
are  also  useful  in  preparing  certain  foods.  Cheese  and 
butter  are  examples. 


372  GENERAL  SCIENCE 

Food  which  we  want  to  keep  for  some  time  must  be 
protected  from  bacteria  or  they  will  cause  it  to  decay. 
This  is  done  by  heating  the  food  and  then  sealing  it, 
or  by  using  a  preservative  in  which  bacteria  cannot 
grow.  Many  of  these  preservatives  are  harmful  to  man 
as  well  as  to  the  bacteria,  and  should  not  be  used. 

QUESTIONS    AND    EXERCISES 

1.  Examine  old  stone  fences  and  the  bark  of  large  trees  to  see  if 
they  are  covered  with  some  greenish  substance.     The  green  material 
consists  of  a  one-celled  alga  called  pleurococcus. 

2.  Visit  a  pond  or  swamp  and  examine  some  pond  scum.     In 
what  way  is  it  useful? 

3.  What  use  is  made  of  mushrooms,  mold,  and  yeast? 

4.  Explain  in  what  way  certain  bacteria  are  more  useful  than 
harmful. 


CHAPTER  XXXVIII 
PLANT   DISEASES   AND    PESTS 

256.  The  low  forms  of  plant  life  are  useful  for  decom- 
posing dead  plants  and  animals,  but  when  they  become 
parasites   on   living  plants   and   animals   then   they   are 
harmful.     Many  fungi  and  bacteria  have  become  true 
parasites  and  live  on  the  higher  plants  cultivated  by  man. 
The  plant  on  which  a  parasite  lives  is  called  the  host.  The 
most  destructive  parasitic  plants  are  rusts,  smuts,  mil- 
dews,  and  blight-producing  fungi  and  bacteria.     These 
parasites  attack  cultivated  grains,  fruits,  and  vegetables, 
and  the  damage  done  by  them  annually  amounts  to  hun- 
dreds of  millions  of  dollars. 

257.  Wheat  Rust.  —  Wheat  rust  is  considered  one  of 
the  most  destructive  parasitic  fungi.     It  passes  part  of 
its  life  on  the  barberry  and  part  on  the  wheat.     It  extracts 
its  food  from  the  leaf  of  the  wheat,  which  is  soon  killed,  so 
that  no  grain  is  produced.     Damp,  warm  weather  is  favor- 
able for  its  growth,  and  a  crop  of  wheat  may  be  killed  in 
a  week.     About  the  only  remedy  is  to  remove  the  bar- 
berry.    Other  wheat  rusts,  not  so  destructive,  live  entirely 
upon  wheat.     The  remedy  for  these  is  not  to  sow  wheat 
on  the  same  ground  many  years  in  succession. 

258.  Apple  Rust.  —  The  life  history  of  the  apple  rust 
or  cedar  rust  is  given  in  detail,  in  order  to  show  how  to 
kill  or  control  it,  and  also  to  serve  as  a  type  in  under- 
standing the  nature  of  a  double  host  parasite. 


374  GENERAL  SCIENCE 

This  parasitic  fungus  attacks  both  the  apple  and  the 
cedar.  On  the  cedar  it  produces  brown,  corky  galls  or 
knots,  called  cedar  apples  or  cedar  flowers.  These  galls 
are  comparatively  slow  in  developing,  and  a  cedar  tree 
which  becomes  infected  in  July  or  August  of  one  year  does 
not  show  any  noticeable  effects  until  May  or  June  of  the 
following  year.  At  this  time  the  young  galls  may  be 
noted  as  small  green  or  greenish-brown  enlargements, 
and  they  do  not  complete  their  de- 
velopment until  the  next  spring,  when 
they  produce  spores  to  infect  the 
apple. 

The  spores  which  the  cedar  apples 
finally  produce   are   only  about  one- 
thousandth  of    an   inch    long   and  a 
little  less   in   width.     They  serve  to 
propagate  the   fungus    in    much  the 
CEDAR  APPLE          same    way    as    seeds    reproduce    the 
Which  produces  spores  higher    plants.      These    spores,    like 

that  cause  apple  rust.  . 

seeds,  will  germinate  and  grow  if  they 
find  favorable  conditions.  They  require  the  young, 
growing  leaves  of  certain  varieties  of  apples  as  a  place 
in  which  to  grow,  and  they  must  receive  moisture  within 
a  comparatively  short  time  or  they  will  dry  up  and  die. 
The  spores  germinate  in  from  three  to  five  hours  by  sending 
out  a  germ-tube  which  penetrates  the  tender  leaf  just  as 
an  ordinary  plant  root  would  go  into  the  soil,  and  when  it 
once  gets  into  the  leaf,  it  cannot  be  killed  by  spraying. 
This  thread-like  growth  absorbs  its  nourishment  from  the 
apple  leaf,  and  the  plant  food  which  should  be  used  in 
fruit  formation  or  tree  growth  is  used  by  the  fungus. 
The  tiny  threads  slowly  work  their  way  around  in  the 
leaf  tissue,  but  do  not  produce  a  visible  spot  for  about 


PLANT  DISEASES  AND   PESTS  375 

ten  days.  Such  spots  soon  assume  a  characteristic  yellow 
color  and  become  slightly  swollen  on  both  the  upper  and 
lower  surfaces.  These  leaf  spots  mature  rapidly,  and 
within  about  two  months  they  send  out  clusters  of  cylin- 
drical fruiting  bodies  on  the  under  surface  of  the  leaf. 
The  fungous  spores  which  are  borne  in  these  fruiting  bodies 
are  not  able  to  grow  on  apple  foliage,  but  they  are  carried 
to  the  cedar  trees  and  again  produce  the  cedar  apples. 

The  damage  done  by  apple  rust  is  very  extensive.  In 
some  cases  entire  crops  of  York  Imperial  apples  are  lost. 
Some  varieties  are  injured  more  than  others.  The 
remedy  is  to  remove  all  red  cedars  frcm  which  the  wind 
can  blow  the  spores  to  the  orchard,  and  to 
spray  the  apple  trees  with  lime-sulphur  solu- 
tion, 1-40,  about  five  to  seven  times  in  five 
weeks,  beginning  when  the  blossom  buds 
show  bright  colors.  Bordeaux  mixture  is 
almost  as  good  as  lime  sulphur. 

259.  Brown  Rot.  —  Brown  rot  is  a  fun- 
gous disease  which  attacks  stone  fruits,  being 
most  destructive  on  plums  and  peaches.  It 

also  attacks  apples  and  pears.     The  chief 

rr  BROWN  ROT 

symptom  of  this  disease  is  the  appearance  Themummies 
of  a  brown-colored  rot .  in  the  fruit.  It  that  carry  the 
may  appear  while  the  fruit  is  still  green  ^f^™*11 
or  on  ripened  fruit.  Sometimes  it  makes 
its  appearance  after  the  picked  fruit  has  been  sent  to 
market.  It  causes  ripened  fruit  to  decay  very  rapidly. 
As  the  disease  progresses  on  green  fruit,  tiny,  gray,  spore 
masses  break  through  the  skin  and  the  wind  scatters 
spores  by  the  thousand  to  other  fruit.  The  rotted  green 
fruit  soon  shrivels  and  dies,  and  may  fall  to  the  ground 
or  hang  on  the  trees.  The  dried  fruit  on  the  trees,  known 


376  GENERAL  SCIENCE 

as  mummies,  under  the  influence  of  the  warm  spring 
rains,  develops  masses  of  new  spores,  which  when  carried 
by  the  breeze  to  blossoms  and  green  fruit  start  the  rot 
anew.  The  mummies  which  fall  to  the  ground  and  become 
only  about  half-covered  produce  spores  which  cause 
blight  of  the  blossoms. 

Remedy.  —  Gather  all  mummies  from  the  trees  and 
ground  and  either  burn  them  or  bury  them  more  than  six 
inches  deep.  Spray  dormant  trees  with  lime-sulphur 
solution,  1-8,  to  kill  spores  adhering  to  the  limbs.  Self- 
boiled  lime-sulphur  spray  will  help  to  protect  peaches  in 
the  summer.  Remove  all  fruit  noticeably  affected  to 
prevent  the  development  of  new  spores. 

260.  Pear  Blight.  —  Pear  blight  is  a  disease  caused  by 
bacteria.  It  is  also  called  fire  blight.  It  sometimes 
attacks  rapidly  growing  apple  and  plum  trees.  It  is 
easily  recognized  by  the  sudden  death  of  blossoms  and 
ends  of  growing  twigs.  The  attacked  leaves  turn  black 
and  cling  to  the  twigs  after  the  other  leaves  have  fallen. 
Sometimes  the  disease  runs  down  the  limbs  and  kills  the 
whole  tree.  Dead  spots  or  cankers  are  formed  on  the 
limbs  and  bodies  of  trees  at  the  base  of  blighted  spurs  and 
watersprouts.  At  times  the  fruit  is  affected  and  dries  on 
the  tree. 

The  bacterium  lives  over  the  winter  in  the  cankers. 
In  the  spring,  sticky,  milky  drops,  containing  many 
bacteria,  run  out  from  these  hold-over  cankers.  Insects 
of  various  kinds  carry  the  bacteria  from  the  cankers 
to  the  flowers  and  tips  of  growing  twigs.  The  feet 
of  the  insects  make  very  slight  wounds  into  which  the 
bacteria  can  pass,  and  then  the  bacteria  multiply  rapidly, 
causing  the  blight  to  become  visible  in  from  ten  to  four- 
teen days. 


PLANT  DISEASES   AND   PESTS 


377 


Remedy.  —  The  diseased  limbs  and  twigs  should  be 
removed  as  soon  as  discovered,  always  cutting  several 
inches  below  the  noticeable  affection  to  be  sure  to  remove 
all  bacteria.  Always  disinfect  the  cut  surfaces  and  also 
the  cutting  instrument  after  each  cut.  The  cankers  in 
which  the  bacteria  live  through  the  winter  can  be  cut  off 
with  a  sharp  knife.  Cut  well  back  into  -the  healthy  bark, 
scrape  out  the  diseased  parts 
thoroughly,  and  sponge  the 
wound  with  corrosive  subli- 
mate solution,  one  part  to 
1,000  parts  of  water.  After 
the  wound  is  dry,  keep  it 
painted  with  good  lead  paint 
until  the  wound  is  healed 
over. 

261.  Other  Diseases  of 
Plants.  —  There  are  many 
other  diseases  caused  by 
parasitic  plants.  Bacteria 
produce  the  diseases  known 
as  blight  of  beans,  cucumber 
wilt,  soft  rot  of  turnips,  black  rot  of  cabbage,  crown  gall 
of  peaches,  pears,  and  apples. 

Additional  diseases  caused  by  fungi  are  apple  scab, 
which  passes  the  winter  on  fallen  leaves;  potato  scab, 
which  is  largely  propagated  by  being  planted  with  the 
potato;  and  blight  of  potatoes. 

Apple  scab  attacks  the  leaves  and  young  apples  about 
blossoming  time.  Spraying  just  before  blossoming  and 
just  after  will  largely  control  the  scab. 

Potato  scab  lives  over  the  winter  on  the  potatoes  and 
also  in  the  soil  in  which  the  potatoes  grew.  It  can  be 


SAN  JOSE  SCALE 
Natural  size  on  the  left;  much 
enlarged  on  the  right. 


378 


GENERAL   SCIENCE 


controlled  by  treating  the  "seed"  potatoes  with  formalin 
solution  before  planting,  and  by  rotation  of  crops. 

Potato  blight  attacks  the  leaves  of  the  potatoes  and 
causes  them  to  die.  It  can  be  prevented  by  keeping  the 
potatoes  covered  with  Bordeaux  mixture  to  prevent  the 
entrance  of  the  fungus  spores.  About  five  sprayings 

are  necessary,  but 
one  or  two  more 
are  sometimes 
given. 

262.  Insect  Pests. 
-The  animal  pests 
which  injure  culti- 
vated plants  are 
mostly  insects.  The 
San  Jose  scale, 
which  is  a  sucking 
insect,  reproduces 
very  rapidly  and  is 
very  destructive  to 
both  peach  and 
apple  trees.  It  can 
be  killed  by  spray- 
ing with  strong  lime-sulphur  solution  when  the  leaves 
are  off  of  the  trees.  Spray  that  is  strong  enough  to  kill 
the  scale  will  also  kill  the  leaves. 

The  codling  moth,  a  small  insect,  is  very  destructive 
to  apples  and  pears.  The  adult  moth  deposits  its  eggs  on 
the  young  apple  just  after  blossoming.  The  egg  hatches 
and  the  larva  crawls  to  the  blossom  end  of  the  apple  and 
eats  its  way  into  it.  The  apples  thus  attacked  usually 
fall  when  they  are  about  the  size  of  thimbles.  About  this 
same  time  the  worm  or  larva  reaches  its  growth  and 


STAGES  OF  THE  CODLING  MOTH 
(a)  the  moth  or  adult  insect,  slightly  en- 
larged; (b)  the  egg,  greatly  enlarged;  (c)  the 
full-grown  larva,  slightly  enlarged;  (d)  the 
pupa,  slightly  enlarged;  (e)  the  pupa  in  its 
cocoon  on  the  inner  surface  of  a  piece  of  bark, 
reduced  about  one-half;  (/)  moth  on  bark  and 
empty  pupa  skin  from  which  it  emerged,  about 
natural  size. 


PLANT  DISEASES  AND   PESTS  379 

emerges  from  the  apple  to  find  a  favorable  place  to  go  into 
the  pupa  stage.  During  the  pupa  stage,  wings  and  other 
adult  parts  of  its  body  are  developed.  It  comes  out  an 


APPLES    RIGHT   FOR 

SPRAYING  CODLING  MOTH  LARVA 

To  kill  the  codling  moth.  And  its  work. 

adult   in   time    to   produce    a    second  generation  in  the 
apples  that  escaped  the  first  attack. 

Remedy  --  Spray  apple  trees  with  a  poison  such  as 
arsenate  of  lead  just  as  the  petals  are  falling  from  the 
blossoms,  forcing  the  spray  well  into  the  blossom  end  of 
the  apple.  Spray  again  about  the  middle  of  the  summer, 
if  necessary,  when  the  second  generation  of  the  moth 
appears. 

QUESTIONS   AND    EXERCISES 

1.  When  is  a  plant  a  parasite?     Name  some  parasites.     What  is 
the  plant  called  on  which  parasites  grow? 

2.  Examine  the  under  side  of  some  growing  leaves  for  a  yellow 
substance.     What  is  it? 

3.  Give  the  life  history  of  the  apple  rust.     Examine  some  green 
apple  leaves  and  cedar  trees  to  determine  the  various  stages  of  the 
apple  rust.     How  can  it  be  destroyed? 

4.  Examine  peach,  plum,  and  cherry  tree  sfor  brown  rot,    What 
remedy  can  be  used? 


380  GENERAL  SCIENCE 

5.  During  the  summer  watch  pear  trees  for  dead  twigs  caused  by 
pear  blight.     What  is  the  best  remedy? 

6.  Examine  trees  for  various  kinds  of  scale  insects.     Which  is  the 
most  destructive? 

7.  Winter  apples  sometimes  contain  "  worms."     What  is  the  name 
of  the  "worm"?     How  did  it  get  there?     What  is  the  best  method 
of  destroying  this  insect? 


CHAPTER  XXXIX 
THE   ANIMAL    SERIES 

263.  We  have  already  learned  from  our  study  of  plants 
that  they  vary  in  size  and  structure  from  the  one-celled 
bacteria  to  the  many-celled  giant  trees  of  the  forest.     Ani- 
mals  also   vary  in  number   of   cells   and   complexity   of 
structure  from  the  one-celled  microscopic  animals  to  the 
largest  and  most  complex  type.     This   chapter  gives  a 
general  view  of  the  animal  life  of  the  world  by  studying 
the  animals  in  groups  arranged  approximately  according 
to  their  complexity.     All  animals  can  be  divided  into  two 
groups  —  the    one-celled    animals    and    the    many-celled 
animals.     The  many-celled  animals  can  be  divided  into 
a  great  many  subdivisions,  such  as  worms,  insects,  crus- 
tacea,  fish,  amphibia,  reptiles,  birds,  and  mammals. 

264.  Protozoa    or    One-celled    Animals. -- There    are 
many  one-celled  animals  which  can  be  found  in  stagnant 
water  such  as  that  found  in  swamps  or  ponds.     There 
are  two  one-celled  animals  which  can  be  easily  found  and 
of  which  we  shall  here  make  a  careful  study.     The  simpler 
of  these  two  is  the  amoeba.     It  is  a  mass  of  protoplasm, 
somewhat  granular  in  structure,  which  has  no  definite  form 
or  shape  and  moves  about  by  putting  out  projections,  and 
when  it  encounters  any  food,  such  as  bacteria,  it  rolls 
itself  about  them  and  thus  takes  the  bacteria  within  its 
own  protoplasmic  body.     It  absorbs  the  food  value  of 
the  bacteria  and  discards  the  waste  matter  chiefly  through 
the  part  of  its  body  called  the  contractile  vacuole. 


382 


GENERAL  SCIENCE 


Its  method  of  reproduction  is  mostly  by  simple  division. 
As  it  absorbs  food  it  increases  in  size  until  it  reaches  the 
stage  at  which  it  divides  into  two  equal  parts,  forming 
two  new  amcebce.  These  two  new  amoebae  eat  and  grow  in 


THE  WAY  AN  AMOEBA  GETS  ITS  FOOD 

like  manner  as  the  parent  until  they  reach  maturity,  when 
they  divide  the  same  as  the  parent  amoeba.  After  the 
amoeba  has  divided  from  fifty  to  one  hundred  times,  a 
complex  process  takes  place  during  which  there  is  a  re- 
vitalization  of  the  animal  in  order  to  increase  its  capacity 
for  reproduction  by  simple  division.  This  complex 
process  is  thought  to  be  a  sexual  process.  There  are 
several  stages  through  which  the  amoeba  passes,  and  it 
is  thought  that  in  some  of  these  stages  it  is  able  to  live 
as  a  parasite  on  higher  animals,  causing  disease.  The 

amoeba  has  no  particular 
value  to  man  except  that 
it  devours  a  great  many 
bacteria  which  may  be 
harmful. 

The  second  one-celled  an- 
imal which  can  easily  be 
found  is  the  paramecium,. 
It  can  be  grown  in  what  is  known  as  a  hay  infusion. 
Place  a  small  handful  of  ordinary  hay  in  a  jar  and 
cover  it  with  water.  In  a  few  days  bacteria  will  cause 
the  hay  to  decompose,  the  water  will  change  color,  and 


PARAMECIA 


THE  ANIMAL   SERIES  383 

the  bacteria  will  collect  on  the  top  of  the  water  in  a 
mass,  making  a  scum.  The  few  paramecia  that  were 
on  the  hay  will  regain  active  life  and  start  to  eat  the  bac- 
teria collected  on  the  top  of  the  water.  If  a  drop  of  this 
scum  is  placed  on  a  glass  slide  and  observed  with  a  mi- 
croscope, a  great  many  one-celled  animals,  granular  in 
structure,  will  be  seen  moving  about  very  rapidly  in  the 
microscopic  field;  these  are  paramecia.  They  are  able 
to  move  by  lashing  the  fine  hair-like  projections  of  the 
protoplasm  of  their  bodies.  These  hair-like  projections 
are  called  cilia  and  are  not  ordinarily  visible  under  the 
microscope. 

The  paramecia,  like  the  amoeba,  reproduce  by  simple 
division,  forming  two  new  animals.  The  two  young 
paramecia  grow  to  maturity  after  feeding  for  some  time, 
and  then  divide  again.  After  a  number  of  generations 
have  been  produced,  two  paramecia  of  about  equal 
size  join  together  and  exchange  a  part  of  their  nucleus 
protoplasm.  This  exchange  of  nucleus  protoplasm 
increases  their  vitality  so  that  they  are  able  to  increase 
more  rapidly  by  simple  division.  This  exchange  of 
nucleus  protoplasm  is  thought  to  be  a  sexual  process. 

The  paramecium  is  somewhat  more  complex  than  the 
amoeba,  although  it  is  a  one-celled  animal.  It  has  a 
special  place  through  which  to  take  in  food,  called  its 
mouth.  It  also  has  special  organs  of  locomotion,  called 
cilia,  and  the  part  of  its  body  used  for  throwing  off  waste 
matter  is  called  the  contractile  vacuole. 

Its  value  to  man  is  of  very  slight  importance.  Its 
only  known  uses  are  to  dispose  of  bacteria  which  collect 
on  stagnant  water  and  to  serve  as  food  for  fish  and 
tadpoles. 

Of  the  other  one-celled  animals  there  are  some  which  are 


384  GENERAL   SCIENCE 

very  useful  to  man  but  very  difficult  to  obtain.  Some  of 
these  have  lived  in  such  great  numbers  that  the  skeleton- 
like  forms  of  their  bodies  have  formed  great  deposits  in 
various  parts  of  the  world.  The  most  widely  used  of 
these  deposits  is  chalk,  of  which  crayon  for  writing  on  the 
blackboard  is  made.  There  are  great  deposits  of  chalk 
in  the  central  and  southern  United  States  and  also  in 
England.  Another  one-celled  animal  forms  deposits  of 
quartz-like  material. 

265.   Worms.  —  The  worm  which  is  most  easily  found 
and  studied  is  the  common  earthworm.     It  lives  in  the 


Intestine  Gizzard         Crop  Gullet          Pharynx 


outh 


FOOD  TUBE  or  AN  EARTHWORM  AND  THE  RINGS  OR  SEGMENTS 

INTO    WHICH   ITS    BODY   IS    DIVIDED 

soil  but  is  found  in  greater  abundance  where  the  soil  is 
fertile.  It  burrows  into  the  earth  by  making  holes  and 
swallowing  the  earth  as  it  goes.  It  is  able  to  move  by  two 
actions  of  its  muscles.  It  has  a  layer  of  muscles  run- 
ning lengthwise  of  its  body,  which  shorten  the  worm  when 
they  contract.  Another  layer  of  muscles  runs  around 
its  body  and  lengthens  the  worm  when  they  contract.  It 
also  has  projections  on  the  lower  part  of  its  body  which 
can  be  directed  forward  or  backward  and  prevent  the 
worm  from  sliding  except  in  the  direction  in  which  it 
wants  to  go.  The  worm  is  covered  with  a  slimy,  mucus- 
like  secretion  which  keeps  its  body  moist,  and  on  account 
of  this  moisture  it  is  able  to  take  oxygen  from  the  air;  this 


THE  ANIMAL  SERIES  385 

is  a  form  of  breathing.  During  heavy  showers,  when  the 
worms'  holes  in  the  soil  become  filled  with  water,  the 
worms  come  out  to  the  surface  because  they  cannot  get 
sufficient  oxygen  while  covered'  with  water.  For  this 
reason  great  numbers  can  be  found  on  the  streets  and 
sidewalks  or  on  the  surface  of  lawns  and  parks  after  a 
heavy  rain.  The  worm  has  no  definite  part  of  its  body 
for  seeing,  yet  it  is  sensitive  to  light  and  also  sensitive  to 
touch. 

The  economic  value  of  the  earthworm  to  the  farmer  is 
very  great.  The  holes  which  it  makes  in  the  soil  give 
opportunity  for  soil  ventilation  or  aeration.  It  also  carries 
large  quantities  of  earth  to  the  surface  and  thus  keeps  the 
soil  in  continuous  circulation  or  movement,  making  it 
more  fertile.  The  food  of  the  earthworm  is  mostly  the 
root  hairs  of  growing  plants  or  any  other  organic 
matter  in  the  soil  which  it  swallows  while  burrowing. 

There  are  also  a  great  number  of  other  worms,  such  as 
sandworms.  These  can  be  found  along  the  seacoast  and 
sometimes  along  rivers  and  lakes.  There  are  also  a  great 
number  of  worms  which  are  parasites  to  man.  These 
will  be  studied  later. 

266.  Insects.  —  Of  all  the  animals  now  living,  the 
insect  is  probably  the  most  completely  fitted  for  its 
environment,  and  on  this  account  it  is  winning  its  way  in 
the  struggle  for  life.  An  insect  usually  has  six  legs  and 
three  divisions  of  its  body.  The  three  divisions  are 
known  as  the  head,  the  thorax,  and  the  abdomen.  The 
legs  are  all  attached  to  the  thorax  or  the  middle  division. 
Most  insects  have  two  pairs  of  wings.  Those  which 
have  only  one  pair  of  wings  prominent  have  two  rudi- 
mentary wings  called  "  balancers."  These  can  easily  be 
found  on  the  common  housefly. 


386  GENERAL  SCIENCE 

The  life  history  of  an  insect  is  very  interesting  for 
observation  and  study.  There  are  four  principal  stages 
through  which  the  insect  passes.  First,  the  egg  stage; 
second,  the  larva  stage  or  eating  period;  third,  the  pupa 
stage;  fourth,  the  adult  stage.  During  the  pupa  stage 
the  insect  changes  its  body  from  the  worm-like  form  to 
that  of  the  adult.  In  the  adult  stage  the  insect  has  six 
legs,  usually  two  pairs  of  wings,  and  some  have  a  pro- 
boscis for  eating  liquid  foods,  while  some  do  not  eat  at  all 

in  the  adult  stage.  The  insects 
which  do  not  eat  during  the  adult 
stage  live  only  a  week  or  so.  Flies, 
mosquitoes,  and  some  butterflies 
which  eat  liquid  foods  may  live 
for  months  or  even  over  the  winter 
in  the  adult  stage. 

267.    Crayfish.  —  Crayfish   are 
very  common  and  can  be  found 
in    creeks   and    in    holes    in    the 
ground,  ranging  from  low  swampy 
ground    to    the    hilltops.      Their 
principal  use  to  man  is  as  scav- 
engers, that  is,  they  devour  quantities  of  decaying  ani- 
mal matter  in  the  creeks  or  about  the  holes  which  they 
make  in  the  ground. 

The  body  of  the  crayfish  is  covered  with  a  bony-like 
shell,  an  exoskeleton,  which  serves  to  protect  it  from  its 
enemies.  It  can  swim  backward  very  rapidly  by  swift 
motions  of  its  tail,  which  is  composed  of  several  flat  bony- 
like  parts.  It  has  two  stalked  compound  eyes  which 
enable  it  to  see  in  all  directions,  and  it  is  thus  able  to 
escape  its  enemies.  It  has  five  pairs  of  legs,  all  of  which 
are  attached  to  the  thorax.  The  four  back  pairs  are  used 


THE  ANIMAL  SERIES  387 

mostly  for  locomotion,  while  the  front  pair,  which  are 
very  much  enlarged  at  their  extremity,  are  used  for  grasp- 
ing and  cutting  food  and  also  for  carrying  the  food  to 
the  mouth.  It  has  two  long  projecting  antennae  which 
serve  as  feelers  and  also  for  smelling.  It  moves  forward 
slowly  while  in  search  of  food,  but  in  case  of  danger  it 
moves  backward  swiftly  —  a  motion  caused  by  rapid, 
forward  jerks  of  its  tail  —  and  seeks  protection  under 
stones  or  other  objects  in  the  water,  or  in  the  bottom  of 
its  hole  if  it  happens  to  be  a  land  crayfish.  It  reproduces 
by  depositing  eggs, 
which  are  carried 
about  on  the  under 
side  of  the  body  until 
hatched.  The  young 

crayfish  which  come 

-  Al  A  CRAYFISH  MOVING  BACKWARD 

from    the    eggs  also 

attach  themselves  to  little  projections,  called  swimmerets, 
on  the  under  side  of  the  body  of  the  parent,  until  they 
are  able  to  find  food  and  care  for  themselves. 

The  thorax  of  the  crayfish  is  a  bone-like  armor  which 
extends  from  the  back  around  to  the  bottom  of  its  body, 
but  the  lower  edge  is  not  grown  to  the  body  of  the  crayfish. 
Just  under  this  bony  covering  are  feather-like  projections 
called  gills.  The  blood  flows  through  these  gills  and  takes 
oxygen  from  the  air  in  the  water.  The  crayfish  causes  a 
current  of  water  to  flow  over  these  gills  in  order  to  keep 
a  fresh  supply  of  oxygen  going  into  its  blood  and  carbon 
dioxide  coming  out. 

The  North  American  lobster  is  a  close  relative  of  the 
crayfish.  It  grows  in  the  salt  water  along  the  Atlantic 
coast  in  great  numbers  and  is  a  valuable  source  of  food. 
Various  states  have  different  laws  regulating  the  size 


388  GENERAL  SCIENCE 

of  the  lobster  which  may  be  sold  in  the  markets.  The  state 
of  Maine  forbids  the  sale  of  a  lobster  less  than  four  and 
one-half  inches  from  the  rear  of  the  thorax  to  the  end  of  the 
bony  projection  between  the  eyes,  making  the  entire  lob- 
ster about  ten  and  one-half  inches  in  length.  They  are 
caught  chiefly  by  means  of  traps  4  feet  long  and  18  inches 
in  diameter,  flat  on  the  bottom  and  semi-circular  on  the 
top.  A  net  incloses  each  end  of  the  trap  and  in  the  net 
there  is  a  hole  large  enough  for  the  lobsters  to  walk 
through.  Once  they  are  on  the  inside  they  are  unable 
to  find  their  way  out.  Dead  fish  are  used  for  bait  and  are 
placed  in  the  center  of  the  trap.  The  traps  rest  on  the 
bottom  of  the  ocean,  usually  in  water  from  10  to  50 
fathoms  in  depth.  A  rope  extends  from  the  trap  at  the 
bottom  to  a  float  on  the  surface  of  the  water  so  that  the 
fishermen  can  find  the  rope  and  draw  up  the  trap  contain- 
ing the  lobsters. 

The  lobster,  like  the  crayfish,  molts  very  often  during 
the  earlier  part  of  its  life.  After  becoming  eight  inches  or 
more  in  length  it  molts  once  a  year.  During  the  molting 
season  the  North  American  lobster  moves  near  the  shore, 
where  it  has  more  protection  under  the  rocks  and  is  less 
liable  to  be  attacked  by  fish  which  prey  upon  it  during  this 
season. 

268.  Amphibians.  —  An  amphibian  is  an  animal  which 
lives  part  of  its  life  in  water  as  a  fish  does  and  part  on  land, 
breathing  by  means  of  lungs.  It  also  has  an  internal 
skeleton  instead  of  an  external  skeleton  as.  the  crayfish 
and  insects  have.  Two  common  examples  of  amphibians 
are  frogs  and  toads.  In  the  spring  they  deposit  their 
eggs,  which  are  inclosed  within  a  gelatin-like  substance 
in  order  to  protect  them  from  fish  which  might  eat  them. 
The  eggs  hatch  in  a  very  short  time  and  after  the  young, 


THE  ANIMAL   SERIES 


389 


called  tadpoles,  are  large  enough  to  take  care  of  themselves 
they  emerge  from  this  gelatin-like  substance. 

The  tadpoles  breathe  with  gills  the  same  as  fish,  and  their 
means  of  locomotion  are  nearly  the  same  as  those  of  fish. 
The  tadpoles  live  by  eating  very  small  animals  and  plants 
found  in  the  water. 
The  difference  between 
a  frog  tadpole  and  a 
toad  tadpole  is  that 
the  frog  tadpole  is  grey 
in  color  and  has  a 
longer  body  with  a 
heavier  tail  than  the 
toad  tadpole,  which 
has  a  short,  round  body 
and  a  very  slender  tail, 
and  is  black  in  color. 
The  frog  tadpole  also 
requires  the  whole  sum- 
mer and  sometimes  a 
part  of  two  summers  to 
grow  to  maturity,  while 
the  toad  tadpole  grows 
to  maturity  in  about 
one  half  of  a  summer. 

When  the  tadpoles  reach  what  may  be  called  the  mature 
stage,  the  gills  are  lost  and  lungs  are  developed  within  the 
body;  legs  also  appear,  the  hind  ones  first,  and  the  tail  is  ab- 
sorbed into  the  body,  the  material  being  used  for  the  build- 
ing up  of  the  legs.  After  the  frog  or  toad  has  changed  into 
the  form  of  the  adult  with  lungs  and  four  legs,  it  spends 
most  of  its  life  on  land.  Frogs  spend  much  of  their  time 
sitting  on  the  bank  watching  for  insects.  In  the  winter 


THE  DEVELOPMENT  OF  A  FROG 

i,  eggs;  2,  tadpole;  3,  tadpole  develop- 
ing hind  legs;  4,  same  tadpole  but  larger; 
5,  front  legs  appearing;  6,  tail  being  ab- 
sorbed; 7,  frog  in  adult  form. 


3QO  GENERAL  SCIENCE 

they  hide  in  the  water  and  breathe  through  their  skin; 
since  their  activity  is  slight  they  do  not  require  much 
oxygen.  The  toads  hide  away  in  holes  in  the  ground 
during  the  winter  and  are  in  an  almost  lifeless  condition. 

The  idea  that  it  rains  toads  came  into  existence  because 
the  toad  tadpoles  can  change  from  the  tadpole  stage  to 
the  adult  form  in  about  24  hours.  If  a  rainy  season  or 
heavy  shower  occurs  just  at  the  time  when  they  are 
changing  from  the  tadpole  to  the  adult  stage,  the  roads  or 
fields  about  ponds,  where  the  tadpoles  are  numerous,  are 
alive  with  young  toads  —  hence  many  persons  concluded 
that  the  toads  were  rained. 

269.  Economic   Value   of   Amphibians.  —  Frogs   serve 
as   food  for   man;   they   also   devour  great   numbers   of 
insects  which  would  be  harmful  to  plants  that  man  grows. 
Toads,  since  they  travel  over  land  away   from  the  water, 
are  of  much  greater  value  than  frogs  in  destroying  insects. 
Several  toads  in  a  garden  will  keep  it  almost  clear  of  the 
harmful  insects  which  prey  upon  valuable  plants. 

270.  Reptiles.  —  Common    examples    of    reptiles    are 
snakes,   turtles,   and  alligators.     They  have  an  internal 
skeleton  and  a  scaly  covering;  the  turtles  in  addition  have 
a  bony  covering.     Reptiles  are  close  relatives  of  birds. 
They  reproduce  by  eggs  which  have  a  tough  covering  and 
contain   considerable   food   for   the   young  while  in   the 
process    of    incubation.     Snakes    usually    deposit    their 
eggs  in  holes  made  in  the  ground;    tortoises  do  the  same. 
Some  snakes  are  poisonous,  such  as  the  rattlers,  copper- 
heads, and  blowing  vipers.       The  rattlesnake  makes  a 
noise  with  its  rattles  when  it  is  disturbed,  to  give  warning 
before  it  attempts  to  bite.     An  additional  rattle  is  added 
each  year  after  the  third  year.       Copperheads  give  no 
warning  whatever,  but  conceal  themselves  in  order  to  wait 


THE  ANIMAL  SERIES  391 

for  the  opportunity  to  bite.  Blowing  vipers  make  a 
hissing  noise  as  a  warning  to  an  approaching  enemy. 

The  economic  value  of  reptiles  is  not  very  great.  Snakes 
devour  a  great  many  bugs,  some  insects,  and  many  field 
mice,  which  are  harmful  to  the  crops.  Turtles  serve  as 
food  for  man.  The  skin  of  alligators  is  used  for  making 
various  useful  leather  articles. 

271.  Birds.  —  The  relation  of  birds  to  reptiles  can  be 
observed  by  noticing  the  scales  on  their  feet  and  by  com- 
paring their  eggs  with  the  eggs  of  reptiles.  The  principal 
difference  between  the  eggs  of  birds  and  those  of  reptiles 
is  that  birds'  eggs  have  a  hard,  limy  shell  on  the  outside 
and  a  tough  membrane  inside,  while  the  eggs  of  reptiles 
have  only  a  tough  but  flexible  membrane  for  a  covering. 
Some  fossil  remains  of  birds  have  also  been  found  which 
give  evidence  that  birds  originated  from  reptiles. 

Some  birds  are  more  destructive  than  beneficial;  for 
instance,  the  English  sparrow,  the  crow,  and  the  blackbird. 
The  English  sparrow  was  introduced  into  the  United 
States  in  1850,  at  Brooklyn,  N.  Y.,  in  order  to  destroy  the 
insect  known  as  the  cankerworm,  but  it  soon  changed  its 
habit  of  living  upon  insects  to  that  of  living  upon  grain  and 
seeds,  and  thus  became  a  menace  to  the  welfare  of  the  in- 
sect-eating birds  instead  of  being  an  insect-destroying  bird 
itself.  It  is  able  to  adapt  itself  to  all  the  conditions  of  its 
environment.  It  does  not  migrate,  but  during  the  winter 
finds  shelter  in  and  around  buildings.  In  the  spring  the 
English  sparrow  builds  its  nest,  which  is  very  large;  the 
inside  is  lined  with  soft  feathers;  and  in  it  four  to  six  eggs 
are  deposited.  The  female  incubates  the  eggs  until 
hatched  and  then  the  parent  birds  start  to  feed  the 
young.  Immediately  the  female  again  deposits  eggs  in 
the  nest  with  the  young  sparrows,  which  now  incubate  the 


392  GENERAL  SCIENCE 

eggs  instead  of  this  being  done  by  the  female  sparrow. 
If  a  nest  is  torn  down  in  the  middle  of  the  summer, 
you  will  find  in  it  eggs  and  birds  of  various  ages  up 
to  those  that  are  mature  and  ready  to  fly  out.  This 
method  of  reproduction  makes  the  English  sparrow  very 
prolific  and  it  becomes  a  menace  to  the  welfare  of  all  other 
birds.  Many  states  offer  a  bounty  of  two  cents  a  head  for 
English  sparrows  in  order  to  bring  about  their  destruction. 

The  crow,  a  large  black  bird,  migrates,  going  south  in 
autumn  and  coming  back  in  the  spring.  Crows  are  very 
destructive  to  germinating  corn  in  the  farmers'  fields  in 
the  spring.  Their  diet '  consists  mostly  of  grain,  but 
occasionally  they  take  up  the  habit  of  hawks,  eating  small 
birds  and  even  young  poultry  grown  by  the  farmers. 
They  also  rob  the  nests  of  other  birds.  They  gather  in 
great  flocks  during  their  migrating  season  and  stop 
occasionally  on  the  migrating  tours  in  the  various  grain 
fields  to  gather  their  evening  meals. 

The  blackbird  is  about  half  the  size  of  the  crow.  They 
also  migrate,  traveling  in  great  flocks,  living  largely  upon 
the  farmers'  productions.  About  two-thirds  of  their  diet, 
however,  is  composed  of  insects  and  bugs  of  various 
kinds. 

The  birds  most  valuable  to  the  American  farmer  are 
the  robin,  bluebird,  martin,  and  various  other  kinds  of 
songbirds.  Their  principal  value  is  in  destroying  or 
consuming  great  numbers  of  insects  which  are  harmful  to 
the  crops. 

The  domesticated  birds  which  can  be  found  on  any 
farm  originated  from  various  types  of  wild  birds.  The 
chickens  have  originated  from  a  wild  bird  of  Asia  and 
the  geese  and  ducks  from  various  types  of  the  wild  kind. 
Many  of  the  birds  which  have  given  origin  to  domesticated 


THE   ANIMAL   SERIES  393 

birds  are  the  game  birds  which  are  still  in  existence  in  the 
wild  state.  Some  of  these  are  the  wild  geese,  ducks,  and 
turkeys.  The  quail,  a  game  bird,  does  not  migrate,  but 
adapts  itself  to  its  surroundings  the  whole  year  round, 
living  upon  whatever  it  is  able  to  find,  eating  some  grain 
but  mostly  wild  berries,  seeds  of  wild  plants,  and  insects. 
Wild  geese  and  ducks  migrate  from  north  to  south  with 
the  change  of  seasons.  They  fly  in  flocks,  usually  in 
the  form  of  a  V,  the  leader  of  the  flock  is  at  the  apex  of 
theV. 

272.  Mammals.  —  Mammals  compose  a  group  of  ani- 
mals which  are  the  most  highly  developed  of  all.  The  egg 
produced  by  the  female  is  microscopic  in  size  and  is  fer- 
tilized within  the  body  of  the  mother,  and  there  grows  into 
the  young  animal  with  all  the  parts  of  an  adult.  After 
birth  the  young  are  nourished  for  a  time  by  milk  secreted 
by  the  mammary  glands  of  the  mother.  Examples  of 
mammals  are  the  elephant,  lion,  mink,  cat,  dog,  horse,  cow, 
monkey,  and  man.  A  number  of  the  mammals  are  plant- 
eating  or  live  entirely  on  plants.  Some  of  the  animals 
which  live  upon  plants  serve  as  food  for  those  which  live 
upon  flesh.  Those  animals  which  live  on  other  animals 
acquired  the  habit  of  eating  flesh  because  it  was  more  easy 
to  get  sufficient  food  by  that  method  than  to  gather  their 
nourishment  from  plants.  Some  of  the  flesh-eating  animals 
are  those  of  the  cat  family.  There  are  some  animals 
which  eat  both  plants  and  flesh.  The  domesticated  dog 
and  cat  have  acquired  the  habit  of  eating  both  plant  and 
animal  food.  The  bear  also  lives  upon  plant  and  animal 
food.  The  opossum,  a  native  animal  of  North  America, 
lives  upon  both  plant  and  animal  food. 

Nearly  all  of  the  domesticated  animals  which  man  now 
possesses  originated  from  animals  of  like  kind  living  in 


394  GENERAL   SCIENCE 

the  wild  state.  The  dog  is  supposed  to  have  originated 
from  the  wild  dog,  and  the  cow  from  various  wild  types;  a 
near  relative  of  the  cow  is  the  buffalo.  Wild  cats  are  still 
in  existence  in  various  parts  of  the  Appalachian  Moun- 
tains. Elephants  have  been  domesticated  and  are  very 
valuable  beasts  of  burden.  The  horse  is  a  native  of  North 
America.  It  originated  from  an  animal  about  the  size  of 
a  wolf.  It  had  four  toes  on  each  front  foot  and  three  toes 
on  the  hind  feet.  It  gradually  acquired  the  habit  of  walk- 
ing on  the  middle  toe  of  each  foot.  This  caused  the  bones 
and  hoof  of  the  middle  toe  to  enlarge  and  the  other  toes  to 
decrease  in  size,  so  that  now  they  cannot  be  seen  except 
occasionally  on  some  horses  when  an  extra  hoof  appears. 
The  horses  which  developed  the  bones  of  the  front  toe 
were  more  swift  than  those  which  did  not,  because  they 
had  longer  legs  and  thus  were  able  to  escape  their  enemies 
and  keep  their  kind  in  existence.  The  horse  finally 
migrated  to  the  Asiatic  continent  where  it  was  first 
domesticated  by  man,  and  since  that  time  it  has  been 
greatly  improved  and  many  types  have  been  produced, 
varying  in  size  from  a  pony  of  a  few  hundred  pounds  to 
the  huge  draft  horse  weighing  one  ton. 

All  other  domesticated  animals  which  are  of  economic 
value  have  also  been  greatly  improved  by  the  study  of 
biology,  which  has  enabled  the  farmers  to  control  the 
types  and  kinds  which  they  wish  to  maintain.  Cattle 
have  been  produced  which  weigh  2,000  pounds,  and  some 
have  been  produced  which  are  immune  from  various  kinds 
of  diseases.  The  hog  —  the  pork-producing  animal  — 
has  also  been  greatly  improved,  so  that  it  grows  to  weigh 
several  hundred  pounds  in  less  than  a  year;  some  have 
been  produced  which  weigh  from  600  to  800  pounds  after 
two  or  three  years  of  special  feeding. 


THE   ANIMAL   SERIES  395 

QUESTIONS    AND    EXERCISES 

1.  To  grow  some  one-celled  animals,  place  some  hay,  green  grass, 
or  lettuce  in  water  and  let  it  stand  at  room  temperature  for  a  few 
days.     A  scum  will  appear  on  the  suface  of  the  water.     This  scum  is 
composed  of  bacteria  and  one-celled  animals.     Place  a  drop  of  the 
scum  on  a  microscopic  slide  and  examine. 

2.  Dig  some  earth  worms  and  observe  their  means  of  locomotion 
and  their  habits.     What  do  they  eat? 

3.  Examine  carefully  some  house  flies,  mosquitoes,  or  other  insects 
and  learn  their  parts  and  habits. 

4.  Look  in  creeks,  ponds,  or  swamps  for  crayfish.     Of  what  use 
are  they  to  man? 

5.  Gather  some  eggs  of  toads  or  frogs  and  watch  them  develop 
into  animals.     Of  what  value  to  man  are  frogs  and  toads? 

6.  In  what  way  are  birds  and  reptiles  similar?     How  are  they 
different?     How  are  birds  of  more  value  to  man  than  reptiles? 

7.  How  has  man  changed  the  size  and  shape  of  domesticated 
mammals?    Of  what  value  are  wild  mammals? 


CHAPTER  XL 
ANIMALS   AS    DISEASE    CARRIERS 

273.  Many    bacteria    and    one-celled    animals    have 
become  parasitic  in  their  habits  and  live  in  the  bodies 
of  the  higher  animals,  producing  a  condition  known  as 
disease.     Most  of  these  diseases  can  now  be  cured,  but  a 
few  still  resist  medical  science  and  are  very  dangerous. 
In  order  for  man  to  protect  himself  from  germ  diseases  it 
is  necessary  for  him  to  know  how  germs  are  carried  about 
from  place  to  place.     Some  germs  are  carried  on  the  out- 
side of  the  bodies  of  animals  and  some  are  carried  on 
the  inside.     Those  which  are  carried  on  the  inside   of 
animals  have  a  complicated  life  history.     Part  of  their 
life  is  spent  in  the  animal  and  the  other  part  in  man. 
There  are  also  some  many-celled  animal  parasites  which 
spend  part  of  their  life  in  domesticated  mammals  and  the 
other  part  of  their  life  in  man.     These  parasitic  diseases 
are  obtained  by  eating  the  flesh  of  domesticated  animals. 

274.  The  House  Fly.  —  The  house  fly  is  also  known  as 
the  typhoid  fly  because  it  carries  the  germ  which  pro- 
duces typhoid  fever.     The  typhoid  fly,  in  going  about  in 
various  places  in  search  of  food  and  of  places  for  depositing 
its  eggs,  comes  in  contact  with  a  great  deal  of  filth  and 
decaying  matter;   here  it  often  gets  the  typhoid  germ  on 
some  part  of  its  body,  usually  its  feet.    It  then  goes  into 
the  house  and  may  walk  over  the  food  which  man  eats  or 
the  utensils  from  which  he  eats,  leaving  the  typhoid  germ 


ANIMALS  AS  DISEASE  CARRIERS 


397 


to  be  taken  into  man's  body  with  the  food.     The  only  use 

that  the  house  fly  serves  is  that  of  a  scavenger,  helping  to 

decompose  decaying  organic  matter.     If  the  body  of  a  fly 

is  viewed  under  the  microscope,  it   will    be 

seen   to  be   well   fitted   for   carrying  germs. 

Its  legs  and  feet  are  covered  with  hairs;   and 

its  head  and  proboscis  are  also  very  rough. 

It  has   two   compound  eyes  which  enable  it 

to  see  in  all  directions,  making  escape  from 

its  enemies  easy. 

The  life  history  of  a  house  fly  should  be 
known  in  order  that  we  may  be  able  to 
destroy  it  most  effectively.  It  deposits  its 
eggs  in  garbage  cans  or  in  decaying  matter 
about  barns  and  other  outbuildings  or  even  MAGNIFIED 
in  decaying  logs  in  the  woods.  In  a  day  or  FOOT  OF  A 
so  the  eggs  hatch  and  the  larva  eats  the  ma- 
terial  in  which  it  lives.  The  larva  has  no  legs,  how  it°i 
but  can  move  slowly  by  twisting  and  bending  ted  for  carry- 
its  body.  It  is  white  in  color,  and  in  about  mg  serms- 

five  to  seven  days  grows  to 
maturity,  when  it  is  about 
a  half  inch  in  length.  When 
the  larva  stops  eating,  a 
brown  coating  is  formed  over 
its  body  and  it  is  then  in  the 
LIFE  HISTORY  OF  THE  HOUSE  FLY  pupa  stage.  It  does  not  take 
(a)  Adult.  (b)  Eggs  (c)  The  any  food  while  m  this  CQn_ 
larva  or  grub  stage,  (a)  The  pupa.  ... 

dition,  but  the  six  legs  and 

the  wings,  head,  and  eyes  are  developed.  It  takes  from  five 
to  seven  days  for  it  to  change  from  the  pupa  to  the  adult 
state.  At  the  end  of  the  pupa  stage  the  fly  comes  out 
a  full  grown  adult.  Flies  vary  in  size,  but  this  variation 


HouSE  FLY 
°w 


398 


GENERAL  SCIENCE 


is  due  to  the  quantity  of  food  eaten  during  the  growing 
period.  After  the  fly  has  been  in  the  adult  stage  for  two 
or  three  days,  eggs  are  again  deposited,  making  a  complete 
generation  in  from  12  to  16  days.  It  is  possible  to  have  as 
rrany  as  eight  or  ten  generations  of  flies  in  one  summer. 

The  house  fly  can 
easily  be  destroyed  by 
removing  or  covering 
all  places  where  it  is  in 
the  habit  of  depositing 
eggs,  thus  preventing 
their  production.  It 
can  also  be  destroyed 
in  the  adult  stage  by 
poisons  and  traps  and 
various  other  means 
which  man  has  devised 
for  the  purpose. 

275.  Mosquitoes.  - 
The  life  history  of  the 
mosquito  is  similar  to 
that  of  many  other 
insects.  Their  eggs  are 
laid  on  water  and  in  a 

(a)  Raft    of    eggs,     (b)  Eggs     enlarged.     ,  ,  hutrh 

(c)    Larvae  or   wrigglers,      (d)  and   (e)    are    day    °r   SO    tney    natctl 

larvae   enlarged.     (/)  Pupa;  (g)  and  (ti)  and  the  larvae  emerge. 

are  females,     (f)  is  a  male.  The     Iarv2£     feed    upon 

bacteria  in  the  water,  and  in  a  few  days  they  change 
from  the  larva  stage  to  the  pupa  stage.  The  larvae 
are  commonly  known  as  wrigglers  and  hang  under 
the  surface  of  the  water  with  their  heads  downward, 
breathing  through  a  tube  in  their  posterior  end,  which 
they  extend  just  above  the  surface  of  the  water.  If 


LIFE  HISTORY  OF  THE  MOSQUITO 


ANIMALS  AS  DISEASE   CARRIERS  399 

the  water  is  covered  with  oil,  the  larvae  are  unable 
to  breathe  through  this  tube  and  so  they  die.  When 
the  larvae  change  to  the  pupa  stage  they  still  remain 
under  the  surface  of  the  water,  breathing  through 
a  tube,  but  they  do  not  eat.  In  the  pupa  stage,  wings 
and  legs  and  other  necessary  organs  for  the  activi- 
ties which  they  perform  during  the  adult  period  are  de- 
veloped. The  adult  mosquito  flies  about  and  lives  as  a 
parasite  upon  other  living  animals  by  forcing  its  proboscis 
into  the  skin  of  the  animal  and  extracting  blood.  This 


MOSQUITOES  IN  RESTING  POSITION 

On  the  left  the  malarial  mosquito  (Anopheles);  on  the  right  the  harmless 
mosquito  (Culex)  (From  Howard's  Mosquitoes). 

habit  of  obtaining  food  makes  it  possible  for  the  mosquito 
to  carry  a  disease  from  one  person  to  another.  If  the 
A  nopheles  mosquito  secures  a  meal  of  blood  from  a  person 
who  has  malaria  fever,  it  will  take  some  of  the  germs  into 
its  body;  these  will  pass  into  the  stomach,  thence  into 
the  blood  of  the  mosquito,  and  into  its  salivary  glands, 
and  then  when  it  bites  or  secures  a  meal  from  a  person 
who  does  not  have  malaria  fever,  some  of  these  germs  are 
forced  out  from  its  salivary  glands,  thus  conveying  the 
germs  to  a  healthy  person,  who  then  becomes  a  subject  of 
the  disease.  The  mosquito  known  as  the  Culex  does  not 
carry  any  disease.  The  Culex  lays  its  eggs  in  rafts,  usually 


400  GENERAL  SCIENCE 

two  rows  side  by  side,  the  eggs  standing  on  end,  while 
the  Anopheles  lays  its  eggs  singly  and  not  in  groups. 
The  body  of  the  adult  Culex  is  in  a  horizontal  position 
when  at  rest,  while  the  body  of  the  Anopheles  is 
almost  vertical  when  at  rest.  The  yellow  fever  mosquito, 
or  the  Stegomyia,  carries  the  yellow  fever  germ  much  the 
same  as  the  Anopheles  carries  the  malaria  germ.  It 
secures  a  meal  from  a  person  who  has  the  yellow  fever.  It 
takes  the  yellow  fever  germ  into  its  body  and  is  then  able 
to  transmit  those  germs  into  the  bodies  of  persons  who  do 
not  have  the  disease.  Yellow  fever  used  to  be  very  com- 
mon in  our  Southern  states  and  in  the  Panama  Canal 
zone;  but  the  destruction  of  the  mosquito  in  these  regions 
has  almost  eliminated  the  disease.  There  are  three 
methods  which  are  used  for  the  destruction  of  the  mos- 
quito, (i)  Keep  the  water  in  swamps  and  streams 
covered  with  oil  so  that  the  larvae  cannot  breathe. 
(2)  Drain  the  swamps  wherever  possible  so  that  the 
mosquito  cannot  find  a  favorable  place  for  depositing  its 
eggs.  (3)  Keep  the  water  stocked  with  fish  which  eat 
the  larvae  of  the  mosquitoes. 

276.  The  Rat  and  Flea.  —  The  rat  is  a  native  of  China 
and  has  moved  westward  over  the  Asiatic  and  European 
continents.  It  came  to  the  United  States  in  1775,  and 
in  75  years  worked  its  way  across  North  America  to  San 
Francisco.  It  was  definitely  learned  in  1907  that  the 
rat  carries  a  very  destructive  disease.  This  disease 
almost  depopulated  many  cities  in  Europe  during  the 
past  centuries;  the  cause  of  the  disease  was  not  known 
at  that  time.  Many  superstitious  people  thought  that 
it  was  a  plague  visited  upon  the  people  by  God  for  their 
sins.  The  disease  is  known  as  the  Bubonic  plague  or 
Black  Death,  and  about  95  per  cent  of  those  who 


ANIMALS  AS   DISEASE   CARRIERS  401 

contract  it  die.  The  germ  does  not  seem  to  have  any 
injurious  effect  upon  the  health  of  the  rat.  The  flea, 
which  is  an  external  parasite  of  the  rat,  will  carry  the 
Black  Death  germ  from  the  rat  to  man  when  it  takes  a 
meal  from  the  rat  and  then  an  occasional  one  from  man. 
This  was  proved  in  1907,  when  150,000  rats  were  dissected 
in  San  Francisco.  In  order  to  rid  the  city  of  San  Francisco 
of  the  Bubonic  plague  and  also  of  the  rat,  hundreds  of 
thousands  of  dollars  were  spent.  Ten  million  pieces  of 
poison  were  laid,  and  it  is  supposed  that  more  than  two 
million  rats  were  killed  and  washed  out  into  San  Fran- 
cisco Bay.  It  is  considered  by  some  that  the  enemy 
Black  Death,  which  was  gaining  entrance  into  the  United 
States  through  San  Francisco,  was  more  dangerous  than 
the  combined  army  and  navy  of  the  most  powerful  nation 
of  the  world.  In  Havana,  in  1914,  twenty  city  squares 
were  depopulated  and  the  rats  driven  out  in  order  to  erad- 
icate the  germs  of  the  Bubonic  plague.  In  order  for  man 
to  be  secure  from  the  Bubonic  plague  it  will  be  necessary 
for  him  to  make  war  on  the  rat  until  it  is  exterminated. 
277.  The  Hog.  --The  hog  carries  two  parasites  which 
affect  the  health  of  man:  viz.,  the  tapeworm  and  the 
trichina.  The  eggs  of  the  tapeworm  are  eaten  by  the 
hog.  These  hatch  within  its  stomach  and  pass  through 
the  walls  of  the  digestive  organs  and  find  their  way  into 
the  muscle  of  the  hog.  If  these  microscopic  worms  in  the 
muscle  of  the  hog  are  eaten  by  man  while  the  meat  is 
uncooked,  the  worm  will  be  released  by  the  digestive 
juices  and  will  attach  itself  to  the  walls  of  the  digestive 
organs  and  become  a  parasite  of  man,  where  the  worm 
increases  in  length  and  width,  sometimes  attaining  a 
length  of  40  feet.  A  tapeworm  can  also  be  taken  into 
the  body  from  raw  beef  and  mutton. 


402  GENERAL   SCIENCE 

A  person  may  contract  the  disease  known  as  trichinosis, 
caused  by  the  trichina,  by  eating  raw  pork.  The  micro- 
scopic worm  incloses  itself  within  the  muscles  of  the  hog 
and  when  eaten  the  juices  in  the  digestive  organs  of  man 
release  it  and  it  finds  its  way  out  of  the  digestive  organs 
into  the  muscles,  where  it  produces  inflammation.  The 
disease  is  very  often  fatal. 

278.  Hookworm.  --The  hookworm  disease  is  common 
in  the  poorer  sections  of  the  Southern  states.  The  worm 
requires  a  warm  climate  in  order  that  it  may  live  over  the 
winter  in  the  soil.  While  young,  it  is  microscopic  in  size 
and  enters  the  body  through  the  soles  of  the  feet  of  those 
\  \  people  who  do  not  wear  shoes  during  the 
J  J  warmer  season.  It  finds  its  way  into  the 
/  /  blood  vessels  and  is  carried  to  the  heart  and 
HOOK  WORMS  tnence  to  tne  lungs;  it  then  passes  out  into 

Actual  size.  the  air  tubes  and  is  coughed  up  into  the 
(Adults)  throat  and  swallowed.  It  attaches  itself 
to  the  inside  of  the  digestive  organs,  where  it  lives 
as  a  parasite  on  man,  producing  laziness,  lack  of  am- 
bition, and  a  loss  of  desire  for  bettering  his  condition. 
The  disease  can  be  cured  with  about  fifty  cents' 
worth  of  medicine  and  a  pair  of  shoes  to  prevent  the 
reentrance  of  the  worm,  but  the  people  must  also  be 
taught  to  be  clean  about  their  homes  and  also  to  continue 
wearing  shoes  during  all  seasons  of  the  year.  The  greatest 
task  in  the  way  of  curing  the  southern  people  of  this 
disease  is  in  educating  the  people  who  have  no  desire  for 
anything  better  and  who  lack  ambition.  Educating  such 
a  group  of  people  is  a  very  slow  and  difficult  process 
and  since  they  do  not  have  the  means  and  a  desire  for 
getting  it,  education  is  also  a  very  expensive  process. 
John  D.  Rockefeller  has  given  more  than  one  million 


ANIMALS   AS   DISEASE    CARRIERS  403 

dollars  to  help  remove   this   disease  from  the  people  in 
the  South. 

QUESTIONS    AND    EXERCISES 

1.  What  disease  does  the  house  fly  carry?     How  can  it  be  pre- 
vented?    Where  do  flies  live  during  the  winter? 

2.  Find  some  mosquito  eggs,  larvae,  pupae,  and  adults.     How  can 
the  mosquito  be   destroyed?     What  diseases   do   some  mosquitoes 
carry?     Are  there  any  disease-carrying  mosquitoes  in  your  commu- 
nity? 

3.  Give  reasons  why  rats  should  be  destroyed. 

4.  What  diseases  may  be  contracted  by  eating  raw  pork  and  beef? 
Is  dried  beef  raw? 


CHAPTER  XLI 
MAN'S   PLACE   IN    NATURE 

279.  Man  is  the  climax  of  the  whole  creation  series. 
He  has  conquered  all  other  animals,  not  by  physical 
force,  but  by  the  power  of  his  brain,  which  makes  him 
able  to  build  places  for  protection  and  also  machines  both 
for  protection  and  for  doing  various  kinds  of  work  which 
would  be  impossible  for  him  to  do  with  his  hands.  By 
using  clothing,  houses,  and  fire  man  is  able  to  adapt  him- 
self to  all  climates,  varying  from  the  intense  heat  at  the 
equator  to  the  severe  cold  at  the  poles. 

Man  has  learned  to  eat  a  great  variety  of  plant  and 
animal  foods,  which  during  primitive  times  he  gathered 
from  plants  growing  wild  and  from  wild  animals.  He 
gradually  learned  how  to  cultivate  plants  and  to  domes- 
ticate animals.  The  plants  and  animals  have  been  so 
changed  and  improved  by  selection  and  careful  breeding, 
that  one  man  now  can  grow  sufficient  plants  and  animals 
to  feed  many  people.  The  process  of  improvement  by 
careful  selection  and  breeding  has  only  begun,  and  greater 
results  will  be  accomplished  in  the  future  by  the  application 
of  man's  intelligence  and  good  judgment  to  methods  of 
husbandry.  Man  is  using  all  the  available  known  forces 
of  nature  to  maintain  his  own  existence. 

The  greatest  enemies  which  man  must  fight  are  not 
the  large  animals  or  large  plants;  these  he  learned  long 
ago  to  subdue  with  his  invented  machines.  The  animals 


MAN'S  PLACE  IN  NATURE  405 

and  plants  which  are  most  destructive  to  mankind  are 
the  ones  which  are  so  small  that  a  microscope  is  needed 
to  find  them.  These  animals  and  plants  which  have 
become  parasites  to  man  produce  many  dangerous 
diseases;  and  unless  man  is  able  to  adapt  himself  to 
the  conditions  which  these  parasites  produce,  or  can 
exterminate  them  by  preventing  their  growth,  they  will 
greatly  hinder  his  progress  or  may  even  exterminate  him. 
In  order  to  cope  with  these  germs  it  is  necessary  for  every 
person  to  use  all  the  knowledge  which  he  possesses  con- 
cerning how  to  live  so  that  he  may  keep  himself  clean, 
healthy,  and  free  from  all  germs.  The  blood  of  most 
healthy  people  is  able  to  kill  nearly  all  disease  germs  as 
fast  as  they  get  into  their  bodies.  A  person  who  is  indul- 
gent in  several  ways,  or  who  is  in  other  than  good  health, 
cannot  expect  to  be  immune  from  the  attacks  of  disease 
germs.  In  order  to  have  good  health  we  should  be  as 
regular  as  possible  in  our  habits  of  rest,  exercise,  and  times 
for  eating.  The  environment  of  the  places  where  we  rest 
(sleep),  exercise  (work),  and  take  our  meals  has  a  great 
influence  upon  health.  Since  man  is  by  nature  endowed 
with  the  capacity  to  select  or  to  modify  his  environment 
to  some  extent,  it  is  necessary  for  him  to  make  it  as 
favorable  as  possible  for  his  existence. 

The  way  to  change  our  environment  is  to -remove  all 
filth  and  decaying  matter  from  our  homes,  have  the  rooms 
properly  ventilated,  lighted,  and  heated,  make  our  homes 
attractive  and  beautiful  inside  and  outside,  with  flowers 
and  decorations  of  various  kinds,  and  see  that  the  sources 
of  water  supply  such  as  springs  and  wells  are  properly 
covered  and  protected  from  contaminating  sources. 

280.  Selecting  a  Home.  —  Since  so  many  people  change 
their  location  every  year,  it  is  very  important  that  all 


4o6  GENERAL  SCIENCE 

should  know  what  kind  of  an  environment  to  select.  In 
choosing  a  locality  for  home-making  or  a  place  in  which  to 
live,  the  social  or  human  environment  should  perhaps 
receive  first  consideration,  because  the  social  environment 
is  usually  the  hardest  to  change.  The  next  to  receive 
consideration  is  the  nearness  to  swamps  or  standing  water 
where  mosquitoes  can  breed;  then  the  following:  good 
drainage  about  the  home  in  order  to  carry  off  surface 
water  quickly,  proper  elevation  with  reference  to  the  im- 
mediate surroundings,  kind  of  water  and  the  quantity 
available  for  household  purposes,  nearness  to  factories 
or  other  undesirable  institutions  that  hinder  the  comforts 
of  a  happy  home. 

QUESTIONS   AND   EXERCISES 

1.  How  does  man  differ  from  other  animals? 

2.  What  are  the  greatest  enemies  of  man?     What  methods  are 
used  to  overcome  them? 

3.  What  are  the  most  important  things  to  consider  in  selecting  a 
location  for  a  home? 


CHAPTER  XLII 
THE   EARTH   AND    ITS   NEIGHBORS 

281.  The  Earth  is  Very  Old.  —  During  the  past  hun- 
dred years  men  have  studied  the  rock  formations  of  the 
earth,  the  causes  of  volcanoes,  mountain-making,  and  the 
rapidity  with  which  the  mountains  are  worn  away  by 
the  process  of  erosion.  The  facts  which  have  been  thus 
collected  show  that  the  earth  is  many  millions  of  years 
old.  Mountains  have  been  made  by  a  gradual  upheaval 
of  the  earth's  surface,  caused  by  expansion  due  to  heat. 
Mountains  have  also  been  made  by  the  flow  of  lava 
from  volcanoes  and  cracks  in  the  earth  or  sides  of  moun- 
tains. 

The  Appalachian  Mountains  in  the  eastern  part  of  the 
United  States  are  very  old  and  were  once  much  higher  than 
they  are  at  present.  The  Potomac,  Susquehanna,  and 
Juniata  rivers  seem  to  have  cut  across  the  mountain  ridges 
as  fast  as  the  ridges  were  elevated;  this  is  shown  by  the 
gaps  in  the  mountains  through  which  these  streams  flow. 
These  gaps  make  the  construction  of  roads  and  railroads 
very  easy.  They  save  the  trouble  of  going  through  the 
mountains  or  over  them. 

The  Rocky  Mountains,  although  about  three  million 
years  old,  are  young  when  compared  to  the  Appalachians. 
The  Rockies  are  still  in  the  process  of  formation.  Earth- 
quakes are  frequent  along  the  western  coast  and  the  vol- 
cano in  northern  California  which  has  recently  been  active 


408  GENERAL  SCIENCE 

ejected  a  large  amount  of  lava  and  mud  which  covered  a 
large  area;   these  are  evidences  of  mountain-making. 

These  mountains  are  old,  but  the  coal  which  is  now 
mined  in  the  Appalachian  and  Rocky  Mountains  is  older 
and  was  formed  long  before  the  mountains  were  made. 
This  gives  us  a  suggestion  that  the  earth  is  many  millions 
of  years  old. 

282.  The  Earth  and  Sun.  —  During  these  millions  of 
years  while  the  earth  was  in  process  of  changing  its  sur- 
face, it  has  been  moving  around  the  sun,  from  which  it  gets 
heat  and  light.     The  path  of  the  earth  around  the  sun  is 
called  the  earth's  orbit.     The  time  required  for  the  earth 
to  go  once  around  its  orbit  is  called  a  year.     This  orbit, 
though  not  quite  circular,  is  about  184,000,000  miles  in 
diameter,  and  the  sun  is  always  approximately  92,000,000 
miles  distant.     The  diameter  of  the  earth  is  about  8,000 
miles  and  the  diameter  of  the  sun  is  about  860,000  miles. 

283.  The  Earth  and  Moon.  —  The  moon  is  a  spherical 
body  which  moves   around   the   earth   and  it  is   about 
240,000  miles  distant  and  about  2,000  miles  in  diameter. 
The  moon  has  mountains  and  volcanic  peaks  on  it;   these 
can  be  seen  with  a  large  telescope.     There  is  no  evidence 
of  any  water  or  life  on  the  moon.     The  moon  goes  around 
the  earth  once  in  28  days,  making  a  lunar  month,  and  it 
turns  once  on  its  axis  during  the  same  time,  and  on  that 
account  always  keeps  the  same  part  turned  toward  us. 
The  moon's  phases  are  due  to  its  positions  with  respect 
to  the  sun.     When  the  moon  and  sun  are  in  the  same  direc- 
tion from  us,  the  moon  is  said  to  be  dark  and  cannot  be 
seen  because  it  passes  across  the  sky  with  the  sun;  during 
this  time  the  sun  is  shining  on  the  part  of  the  moon  turned 
away  from  us.     When  the  sun  and  moon  are  in  opposite 
directions,  or  nearly  so,  from  us  the  moon  passes  across 


THE  EARTH  AND   ITS  NEIGHBORS  409 

the  sky  at  night  and  the  part  which  is  illuminated  by  the 
sun  is  turned  toward  us  and  reflects  the  sun's  light  to  us 
the  same  as  the  wall  of  a  building  will  reflect  light.  When 
all  of  the  moon  which  is  illuminated  by  the  sun  can  be 
seen,  the  moon  is  said  to  be  full.  When  only  one-half  of 
the  illuminated  part  can  be  seen,  it  is  called  first  quarter 
during  the  light  of  the  moon  and  last  quarter  during  the 
dark  of  the  moon.  The  period  known  as  "  light  of  the 
moon"  lasts  14  days,  extending  from  "new  moon" 


DIAGRAM  OF  AN  ECLIPSE 

Showing  why  an  object  casts  a  shadow  of  two  intensities 
when  in  the  presence  of  a  large  luminous  body  like  the  sun. 

to  "full  moon,"  during  which  time  the  visible  illuminated 
part  is  increasing  in  size.  The  period  known  as  "dark  of 
the  moon"  also  lasts  14  days,  during  which  time  the 
visible  illuminated  part  is  decreasing  in  size. 

284.  Eclipse  of  Sun  and  Moon.  —  The  earth  and  moon, 
like  all  opaque  objects,  cast  a  shadow  in  the  direction 
opposite  the  sun.  Since  the  sun  is  very  large,  being  100 
times  the  diameter  of  the  earth  and  400  times  the  diameter 
of  the  moon,  the  shadows  of  the  earth  and  moon  come  to 
a  point  and  are  cone-shaped.  The  average  length  of  the 
earth's  shadow  is  856,000  miles  and  that  of  the  moon  is 
232,000  miles.  When  the  moon  happens  to  pass  through 
the  earth's  shadow  at  night,  a  part  or  all  of  it  is  invisible 


4io 


GENERAL  SCIENCE 


and  it  is  then  said  to  be  eclipsed.  In  the  day  time  when 
the  moon  is  close  enough  so  that  its  shadow  reaches  the 
earth,  the  sun  is  hidden  from  view  in  that  area  on  which 
the  moon's  shadow  falls,  and  then  the  sun  is  eclipsed. 
Since  the  diameter  of  the  moon's  shadow  where  it  touches 


ECLIPSES  OF  SUN  AND  MOON 

Showing  how  the  sun  is  eclipsed  by  the  shadow  of  the  moon  reaching 
the  earth  and  how  the  moon  is  eclipsed  when  it  passes  through  the  shadow 
of  the  earth. 

the  earth  is  small,  most  of  the  eclipses  of  the  sun  are  only 
partial;   occasionally  a  total  eclipse  occurs. 

285.  The  Planets. -- There  are  other  bodies  moving 
around  the  sun  besides  our  earth.  Seven  of  these  bodies 
and  the  earth  are  called  planets.  Each  one  of  these 
planets  has  a  name  of  its  own.  Two  of  the  planets  are 
closer  to  the  sun  than  the  earth  and  five  of  them  are 
farther  away.  In  the  order  of  their  distance  from  the 
sun  they  are  as  follows:  Mercury,  Venus,  Earth,  Mars, 
Jupiter,  Saturn,  Uranus,  and  Neptune.  The  outer  ones 


THE   EARTH  AND   ITS   NEIGHBORS 


411 


are  so  far  from  the  sun  that  they  do  not  receive  much 
heat  and  light. 

The  time  it  takes  for  these  planets  to  go  once  around  the 
sun  is  given  in  the  following  table  with  the  distance  of 
each  from  the  sun.  The  time  is  represented  in  number  of 
earth's  days  and  years. 

Planets          Time  for  one  revolution         Distance  from  the  sun 
Mercury 88    days 36  million  miles 


Venus 

Earth 

Mars 

Jupiter 

Saturn . . 


225  days 67^ 

36sidays 92 

687  days. .  w  

u|  years 

29!  years 886 


Uranus 84    years 1780 

Neptune 165    years. 2790 


These  planets  with  the  sun  compose  the  solar  system. 
The  entire  solar  system  is  moving  through  space  and  is  one 
system  among  hundreds  of  others.  The  distant  stars 
are  suns  much  larger  than  our  sun,  and  each  one  is  at  the 
center  of  a  system  of  its  own.  The  earth  itself  is  but  a 
small  particle  of  matter  when  compared  with  all  the 
matter  in  the  universe. 

Mercury  and  Venus  do  not  have  moons  or  satellites. 
The  earth  has  one,  Mars  has  two,  Jupiter  has  five,  Saturn 
has  nine,  Uranus  has  four,  and  Neptune  has  one  satellite. 
These  moons  move  around  the  planets  in  much  the  same 
way  as  the  planets  move  around  the  sun.  The  moons  are 
not  self-luminous,  but  only  reflect  the  light  received  from 
the  sun  the  same  as  objects  on  the  earth  reflect  light  to 
our  eyes. 

286.  The  Stars.  —  The  stars  other  than  the  planets 
are  at  a  very  great  distance  from  us,  so  far  that  telescopes 
do  not  make  them  look  much  larger  than  they  do  to  the 
unaided  eye.  When  the  planets  are  viewed  with  a  good 


4i2  GENERAL  SCIENCE 

telescope,  they  appear  like  huge  balls  illuminated.  Some 
of  their  moons  can  also  be  seen. 

It  takes  about  eight  minutes  for  the  light  to  come 
from  the  sun  to  the  earth,  a  distance  of  about  ninety-two 
million  miles.  This  means  that  light  travels  at  the 
enormous  speed  of  186,000  miles  per  second,  or  seven 
and  one-half  times  around  the  earth  if  it  could  go  in  a 
curved  line. 

The  stars  other  than  the  planets  are  called  fixed  stars, 
and  the  nearest  of  these,  Alpha  Centauri,  is  so  far  away 
that  4.4  years  are  required  for  the  light  to  come  from  it 
to  the  earth.  It  takes  about  45  years  for  the  light  to 
come  from  the  North  Star.  Some  of  the  stars  are  so  far 
away  that  several  hundred  years  are  required  for  the  light 
to  reach  the  earth. 

287.  Meteors.  —  Meteors  are  also  known  as  "shooting 
stars."  Some  are  composed  mostly  of  iron  and  others  of 
stone.  They  vary  in  size  from  small  shot  to  hundreds  of 
pounds.  One  found  in  Texas  weighs  1635  pounds;  it  is 
now  in  the  Peabody  Museum  of  Yale  University.  The 
same  museum  has  hundreds  of  smaller  ones  also.  Other 
museums  in  the  United  States  and  Europe  contain  thou- 
sands of  meteorites. 

Meteors  are  flying  through  space  at  a  speed  of  about 
35  miles  per  second,  and  when  they  strike  the  earth's 
atmosphere  they  are  made  white  hot  by  the  impact  and 
by  the  friction  produced  while  passing  into  the  air.  They 
strike  the  earth's  atmosphere  by  the  million  every  day, 
but  nearly  all  are  vaporized  before  they  penetrate  very  far 
and  never  become  visible.  Those  which  are  large  enough 
to  be  seen  rarely  become  visible  until  they  are  within 
70  miles,  and  usually  disappear  before  they  come  within 
30  miles  of  the  earth.  Only  a  few  have  been  seen  to  fall 


THE  EARTH  AND  ITS  NEIGHBORS  413 

to  the  earth.     In  1866  a  shower  of  small  meteors  fell  in 
the  western  part  of  the  United  States. 

QUESTIONS   AND    EXERCISES 

1.  What  evidence  can  you  see  that  the  earth  is  very  old?    How 
were  the  hills,  valleys,  and  plains  made?    When  were  coal,  petroleum, 
limestone,  and  chalk  formed? 

2.  What  causes  the  phases  of  the  moon?     Why  is  the  moon  some- 
times eclipsed?    What  causes  an  eclipse  of  the  sun? 

3.  What  planets  are  going  around  the  sun  other  than  the  earth? 

4.  If  you  were  on  the  moon,  how  would  the  earth  appear  to  you? 

5.  What  is  the  nature  of  a  meteor  or  "  shooting  star  "?    Where 
are  they  when  they  are  visible? 


APPENDIX 
THE    METRIC    SYSTEM 

Historical.  -*-  The  Metric  System  is  an  outgrowth  of 
the  French  Revolution  of  1789.  At  that  time  there  was  a 
general  disposition  to  break  away  from  old  customs;  and 
the  Revolutionists  contended  that  everything  needed 
remodeling.  A  commission  was  appointed  to  determine 
an  invariable  standard  for  all  measures  of  length,  area, 
solidity,  capacity,  and  weight.  After  due  deliberation, 
an  accurate  survey  was  made  of  that  portion  of  the  ter- 
restrial meridian  passing  through  Paris,  between  Dunkirk, 
France,  and  Barcelona,  Spain;  and  from  this,  the  distance 
on  that  meridian  from  the  equator  to  the  pole  was  com- 
puted. The  quadrant  thus  obtained  was  divided  into  ten 
million  equal  parts;  one  part  was  called  a  meter,  and  is  the 
base  of  the  system.  From  it  all  measures  are  derived. 

France  adopted  The  Metric  System  in  1795.  It  is  now 
used  in  nearly  all  civilized  countries.  It  was  authorized 
by  an  act  of  Congress  in  the  United  States  in  1866. 

The  Metric  System  is  a  decimal  system  of  weights  and 
measures.  The  meter  is  the  primary  unit  upon  which 
the  system  is  based,  and  is  also  the  unit  of  length.  It  is 
39.37  inches  long.  The  standard  meter,  a  bar  of  plat- 
inum, is  kept  among  the  archives  in  Paris.  Duplicates 
of  this  bar  have  been  furnished  to  the  United  States^ 

The  names  of  the  lower  denominations  in  each  measure 
of  the  Metric  System  are  formed  by  prefixing  the  Latin 


416 


APPENDIX 


numerals,  deci  (.1),  centi  (.01),  and  milli  (.001)  to  the 
unit  of  that  measure;  those  of  the  higher  denominations, 
by  prefixing  the  Greek  numerals,  deka  (10),  hekto  (ico), 
kilo  (1000),  and  myria  (10,000),  to  the  same  unit.  These 
prefixes  may  be  grouped  about  the  unit  of  measure,  show- 
ing the  decimal  arrangement  of  the  system,  as  follows: 


f  milli    = 

Lower  Denominations  I  centi    = 

(  deci     = 

Unit  of  Measure  = 

deka 
Higher  Denominations 


hekto 

kilo 

myria 


.001 
.01 
.1 
i. 
10. 
100. 
1000. 
i  oooo. 


The  units  of  the  various  measures,  to  which  these  pre- 
fixes are  attached,  are  as  follows: 

The  Meter,  which  is  the  unit  of  Length. 
The  Liter,  which  is  the  unit  of  Capacity. 
The  Gram,  which  is  the  unit  of  Weight. 

The  name  of  each  denomination  thus  derived,  immedi- 
ately shows  its  relation  to  the  unit  of  measure.  Thus,  a 
centimeter  is  one  one-hundredth  of  a  meter;  a  kilogram 
is  a  thousand  grams;  a  hektoliter  is  one  hundred  liters, 
etc. 

Measure  of  Length.  —  The  Meter  is  the  unit  of 
Length,  and  is  the  denomination  used  in  all  ordinary 
measurements. 


10  millimeters,  marked  mm. 

10  centimeters 

10  decimeters 

10  meters 

10  dekameters 

10  hektometers 

10  kilometers 


centimeter,  marked    cm. 


decimeter, 

meter, 

dekameter, 

hektometer, 

kilometer, 

myriameter, 


dm. 
m. 
Dm. 
Hm. 
Km. 
Mm. 


THE   METRIC   SYSTEM  417 

The  centimeter  and  millimeter  are  most  often  used  in 
measuring  very  short  distances;  and  the  kilometer,  in 
measuring  roads  and  long  distances. 

Measure  of  Capacity.  —  The  Liter  (pro.  le'ter)  is  the 
unit  of  Capacity.  It  is  equal  in  volume  to  a  cube  whose 
edge  is  a  decimeter;  that  is,  one-tenth  of  a  meter. 

10  milliliters,  marked  ml.  =  i  centiliter,  marked   cl. 
10  centiliters  =  i  deciliter,  dl. 

10  deciliters  =  i  liter,  1. 

10  liters  =  i  dekaliter,  Dl. 

10  dekaliters  =  i  hektoliter,       "      HI. 

This  measure  is  used  for  liquids  and  for  dry  substances. 
The  denominations  most  used  are  the  liter  and  hektoliter; 
the  former  in  measuring  milk,  vinegar,  etc.,  in  moderate 
quantities,  and  the  latter  in  measuring  grain,  fruit,  etc., 
in  large  quantities.  Instead  of  the  milliliter  and  the 
kiloliter,  it  is  customary  to  use  the  cubic  centimeter  and 
the  cubic  meter  (marked  m3),  which  are  their  equiv- 
alents. 

Measure  of  Weight.  —  The  Gram  is  the  unit  of 
Weight.  It  was  determined  by  the  weight  of  a  cubic 
centimeter  of  distilled  water,  at  the  temperature  of 
maximum  density  (39.2°  F.)  or  4°  C. 

10  milligrams,  marked  mg.  =  i  centigram,  marked       eg. 

10  centigrams  =  i  decigram,  dg. 

10  decigrams  =  i  gram,  g. 

10  grams  =  i  dekagram,  .     Dg. 

10  dekagrams  =  i  hektogram,  Hg. 

10  hektograms  =  i  kilogram,  Kg. 

10  kilograms  =  i  myriagram,  Mg. 

10  myriagrams  or  100  kilograms  =  i  quintal,  Q. 

10  quintals,  or   1000  =  i  metric  ton,  M.T. 

The  gram,  kilogram  (pro.  kil'  o-gram),  and  metric  ton 
are  the  weights  commonly  used.  The  gram  is  used  in  all 


418  APPENDIX 

cases  where  great  exactness  is  required;  such  as,  mixing 
medicines,  weighing  the  precious  metals,  jewels,  letters, 
etc.  The  kilogram,  or,  as  it  is  commonly  abbreviated, 
the  "kilo,"  is  used  in  weighing  coarse  articles,  such  as 
groceries,  etc.  The  metric  ton  is  used  in  weighing  hay 
and  heavy  articles  generally. 

Since,  in  the  Metric  System,  10,  100,  1000,  etc.,  units 
of  a  lower  denomination  make  a  unit  of  the  higher  de- 
nomination, the  following  principles  are  derived: 

Principles.  —  i.  A  number  is  reduced  to  a  lower 
denomination  by  removing  the  decimal  point  as  many 
places  to  the  right  as  there  are  ciphers  in  the  multiplier. 

2.  A  number  is  reduced  to  a  higher  denomination  by 
removing  the  decimal  point  as  many  places  to  the  left  as 
there  are  ciphers  in  the  divisor. 

The  following  table  presents  the  legal  values  of  those 
denominations  of  the  Metric  System  which  are  in  common 
use. 


Denomination 

Legal  Value 

Meter  

39-37       inches 

Centimeter  

..'...            .3937     inch 

Millimeter  

-03937  inch 

Kilometer  

-62137  mile 

Ar                      ........ 

119.6           sq.  yards 

Hektar  

2.471       acres 

Square  Meter  

i  .  196       sq.  yards 

Liter  

1.0567     quarts 

Hektoliter  

2.8375     bushels 

Cubic  Centimeter  

.061       cu.  inch 

Cubic  Meter  

i  .  308      cu.  yard 

Ster  

.2759     cord 

Gram  

I5-432       grains  troy 

Kilogram  

....         2.2046    pounds  av. 

Metric  Ton  

2204.6          pounds  av. 

GLOSSARY 

Abnormal,  not  normal.     Abnormal  foods  are  those  which  are  not  well 

prepared,  excessively  spiced  or  sweetened,  and  things  which  are  not 

necessary  but  may  be  an  injury.     Pies,  some  cakes,  tea,  and  coffee 

are  examples. 
Al'ka  loid,  a  substance  having  an  alkaline  or  basic  property,  found 

in  plants,  usually  combined  with  such  acids  as  tannic,  malic,  or  citric. 

Examples  are  caffine,  theobromine,  morphine,  cocaine,  quinine,  etc. 

Some  alkaloids  are  stimulants  and  some  are  narcotics. 
Am  mo'ni  um  hy  drox'ide,  a  basic  compound  made  by  forcing  ammonia 

gas  into  water.     Household  ammonia  is  an  example. 
Bac  te'ri  a   (singular,  bac  te'ri  um),  one-celled  plants  so  small  that  a 

good  microscope  is  needed  to  see  them.     Most  of  them  have  to  be 

stained  before  they  can  be  seen  individually.     Some  cause  disease, 

some  are  harmless,  and  many  kinds  are  useful. 
Bear'ings  of  a  machine,  the  fixed  parts  or  shafts  on  which  wheels  turn. 

A  wagon  has  sliding  bearings,  a  bicycle  has  ball  bearings,  and  many 

automobiles  have  roller  bearings.     Oil  is  placed  on  the  bearings  so 

that  the  wheels  will  turn  without  much  friction  or  resistance. 
Bordeaux'  mixture  (bor  do'},  a  mixture   of   copper  sulfate,  quicklime, 

and  water.     For  plants  with  tender  leaves,  dissolve  two  pounds  of 

copper  sulfate  in  45  gallons  of  water,  slake  two  pounds  of  quicklime 

in  5  gallons  of  water;  then  mix  the  two  solutions. 
Cal'ci  um,  a  pale  yellow  metal;    a  simple  substance.     It  is  found  in 

nature  combined  with  other  elements*     It  is  one  of  the  component 

parts  of  lime,  limestone,  and  marble. 
Cap  il  lar'i  ty  or  capillary  attraction,  the  peculiar  action  by  which  the 

surface  of  a  liquid,  where  it  is  in  contact  with  a  solid,  is  elevated  or 

depressed.     Water  adheres  to  the  sides  of  a  small  tube  to  such  an 

extent  that  it  is  drawn  up  the  tube.     This  is  one  of  the  forces  which 

cause  sap  to  flow  up  in  a  tree. 
Car'a  mel,  partially  burnt  sugar.     It  can  be  made  by  heating  sugar  to 

200°  C.  for  a  few  minutes.    The  brown  color  of  bread  crust  is  caused 

by  the  formation  of  caramel  during  baking. 
Car'bon  mon  ox'ide,  a  gas  formed  when  carbon  gas  is  only  one-half 

oxidized.     It  is  very  poisonous. 
CC.  or  C.  C.,  a  cubic  centimeter. 
Con  ser  va'tion,   a   process   of   guarding,   protecting,   or   saving  force, 

energy,  and  resources.     To  prevent  the  waste  of  our  forests,  coal, 

and  iron  ore  is  conservation. 


420  GLOSSARY 

Consumption  of  a  gas,  to  burn  it  in  order  to  make  heat  or  light,  or  to 
use  it  for  making  compounds.  Green  plants  consume  carbon  dioxide 
gas  of  the  air  when  they  make  starch.  Animals  consume  oxygen 
when  they  breathe. 

Con  tam'i  nate,  to  infect  with  poisons,  filth,  or  with  disease  germs. 
Surface  water  from  a  house  or  barn  flowing  into  a  well  by  a  short 
passage  may  contaminate  the  water  and  render  it  unfit  for  use. 

De  com  pose',  to  separate  into  simpler  substances  or  parts.  To  de- 
compose water  is  to  separate  it  into  hydrogen  and  oxygen.  Plants 
decompose  when  they  decay. 

Den'si  ty  of  a  substance  is  the  ratio  of  its  weight  in  grams  to  its  volume 
in  cubic  centimeters.  One  cubic  centimeter  of  water  weighs  one 
gram,  hence  its  density  is  one. 

Di'a  phragm,  a  large  thin  muscle  which  forms  a  partition  between  the 
lungs  and  digestive  organs  of  the  human  body  and  assists  in  breath- 
ing. It  is  arched  upward,  and  when  it  contracts  the  chest  cavity  is 
enlarged  and  air  rushes  in  to  fill  the  lungs. 

Di'a  stase,  a  ferment  found  in  cereal  grains.  It  changes  starch  to  sugar 
when  the  temperature  is  right  and  sufficient  moisture  is  present. 
When  conditions  are  favorable  for  plants  to  grow,  diastase  can  act. 

Digestive  fluid,  a  fluid  which  contains  ferments  that  make  food  soluble 
in  water.  Examples.  —  Saliva  in  the  mouth,  gastric  juice  in  the 
stomach. 

Di  lute',  to  make  less  strong  or  less  concentrated.  Vinegar,  ammonia, 
and  alcohol  may  be  diluted  by  adding  water. 

Dis  so  lu'tion,  the  process  of  dissolving  a  crystallized  substance  in  a 
liquid.  Sugar  and  salt  can  be  dissolved  in  water.  Heat  is  often 
required  to  dissolve  a  substance. 

Dis  til  la'tion,  the  process  of  separating  a  substance  which  vaporizes 
easily  from  one  or  more  substances  which  vaporize  less  easily.  The 
vapor,  caused  by  adding  heat,  is  liquified  or  condensed  while  passing 
through  pipes  which  are  kept  cool  by  water  flowing  over  them. 

Elec  tro  mo'tive  force  (abbr.  E.M.F.),  the  force  which  drives  an  electric 
current.  It  is  the  difference  in  potential  or  electrical  pressure  at  two 
points  on  an  electric  circuit.  The  volt  is  the  unit  of  electromotive 
force. 

En  vi'ron  ment  consists  of  the  things  and  conditions  around  you  which 
may  affect  your  life.  It  consists  of  weather,  climate,  plant  life,  ani- 
mal life,  and  the  social  conditions  made  by  man.  Students  in  high 
school  adjust  themselves  to  the  conditions  made  by  themselves  and 
their  teachers,  and  to  the  changes  in  the  weather. 

En'zyme  (en'zim),  a  general  name  for  a  number  of  chemical,  digestive 
ferments,  such  as  diastase  found  in  cereals,  pepsin  and  rennin  fcund 
in  the  gastric  juice  of  the  stomach,  and  ptyalin  in  the  saliva. 

Ex'cre  to  ry  organs  are  organs  which  take  poisons  and  useless  matter 
from  the  body.  Examples  are  the  kidneys,  liver,  lungs,  etc. 

Fehling's  solution.  (Named  after  Hermann  Fehling  (1812-1885),  a 
German  chemist.)  It  is  made  by  dissolving  one  part  by  weight  of 


GLOSSARY  421 

copper  sulfate  (blue  vitriol)  in  14.3  parts  by  weight  of  water.    (Several 

hours   are  required  for  it  to  dissolve.)      Mark  this  solution  No  i. 

Dissolve  one  part  by  weight  of  caustic  soda  and  1.081  parts  of  Ro- 

chelle  salt  in  3.12  parts  by  weight  of  water.     Mark   this  solution 

No.  2.     For  use  mix  equal  parts  of  i  and  2.    When  it  is  heated  with 

certain  sugars,  red  cuprous  oxide  is  formed,  giving  the  characteristic 

red  color  for  the  sugar  test. 
Fer'ment,   an  agent  capable  of    producing  fermentation  or  chemical 

changes  like  those  produced  by  yeast  plants,  diastase,  bacteria,  etc. 

(See  diastase  and  enzyme.) 
Func'tion,  the  use  of  any  organ  or  part  of  an  animal  to  the  animal  itself. 

The  same  application  may  be  made  to  plants. 
Fu'sion,  the  process  of  changing  a  solid  to  the  liquid  condition  by 

means  of  heat.     Some  substances  fuse  at  low  temperatures  and  others 

at  very  high  temperatures. 
Gly'co  gen,    a    white,    tasteless   carbohydrate,    related    to   starch   and 

dextrin  sugar.     It  is  found  in  the  liver  of  animals  and  is  sometimes 

called  animal  sugar,  and  animal  starch. 
Grafting  wax,  a  wax  used  for  holding  grafting  scions  in  position  until 

they  grow.     To  make  it:    Melt  together  one  pound,  of  resin,  one- 
half  pound  of  beeswax,  one-fourth  pound  of  tallow.     Stir  it  for  a  few 

minutes  while  hot.    Pour  the  mixture  into  cold  water.     Grease  your 

hands  and  pull  the  wax  until  it  has  a  straw  color. 
"  High  "  on  a  weather  map  means  that  the  barometers  in  that  area 

read  higher  than  those  which  are  more  distant  from  that  center. 

Fair  weather  usually  follows  in  an  area  marked  "  high." 
Hu'mus,  the  decaying  plant  and  animal  matter  of  the  soil.    It  usually 

gives  the  soil  a  dark  color  and  is  one  of  the  principal  sources  of  plant 

food. 
I'o  dine,  a  simple  substance;    an  element  blackish  gray  in  color.     It 

dissolves  readily  in  alcohol  and  the  solution  is  reddish  violet  in  color. 

In  dilute  form  it  turns  starch  to  a  purple  color. 
Lime  is  made  by  heating  limestone  (CaCO3)  to  a  white  heat  for  about 

two  days  in  a  limekiln  to  drive  off  the  carbon  dioxide.     The  solid 

matter  taken  from  the  limekiln  is  calcium  oxide  (CaO)  or  commercial 

unslaked  lime. 
Lime-sulphur  spray,  a  spray  made  by  boiling  a  mixture  of  quicklime 

and  sulphur  in  water  for  an  hour;   15  pounds  of  each  to  50  gallons  of 

water. 
Linear,  when  applied  to  objects  means  long,  slender  ones  which  are 

comparatively   uniform  in   width.     Linear  expansion  refers  to   the 

expansion  in  the  direction  of  length. 
"Low"  on  a  weather  map  means  that  the  barometers  in  that  area 

read  lower  than  they  do  at  points  more  distant  from  that  center. 

Cloudy  and  rainy  weather  usually  follow  in  a  "  low  "  area. 
Mechanical  advantage  of  a  block-and-tackle  is  an  even  or  odd  number 

according  to  whether  the  rope  is  first  fastened  to  the  fixed  or  movable 

pulleys  respectively. 


422  GLOSSARY 

Mer'cu  ry,  a  silver- white  liquid  metal.  It  freezes  at  —  39.5°  C.  and 
boils  at  357°  C.  Mercury  ore  (cinnabar)  is  mined  in  Spain,  Austria, 
Italy,  and  in  California  and  Texas.  It  is  separated  from  the  ore  by 
roasting  in  closed  ovens  and  then  condensing  the  vaporized  mercury. 
It  is  also  known  as  quicksilver. 

Mil'let,  a  grain  grown  in  Europe  and  Asia  for  food  for  both  animals 
and  man.  Millet  is  also  a  general  name  for  a  number  of  small  grains. 
The  variety  grown  in  the  United  States  is  usually  cut  green  and  fed 
as  hay. 

Mo'ment  of  a  force  is  the  tendency  of  that  force  to  produce  motion  about 
a  point  or  axis.  It  is  the  product  of  the  force  times  the  perpendic- 
ular distance  from  the  point  to  the  line  of  direction  of  the  force.  If 
a  horse  is  pulling  with  a  force  of  400  pounds  on  a  windlass  lever  10 
feet  long,  the  moment  is  4000. 

Neutral  substances,  those  which  do  not  have  characteristics  like  acids 
or  bases.  Common  salt  and  pure  water  are  examples. 

Nu'tri  ents,  the  three  divisions  made  of  nutritious  foods,  namely,  carbo- 
hydrates, fats,  and  protein. 

Nu'tri  ment,  a  food  which  promotes  growth  and  repairs  the  natural 
waste  of  animals  and  plants.  Some  nutriments  contain  all  three 
nutrients. 

Ores  are  compounds  taken  from  the  earth  and  contain  one  or  more 
valuable  metals,  such  as  iron,  copper,  mercury,  silver,  gold,  etc. 

Or'gan  ism,  a  living  body,  as  a  plant  or  animal.  It  may  be  made  up  of 
organs,  tissues,  and  cells.  A  one-celled  animal  or  plant  is  an  organ- 
ism. 

Phe  nol  phthal'e  in  (fe  nol  thal'e  in),  a  very  complex  substance  that 
cannot  be  made  in  the  ordinary  laboratory.  If  purchased  in  dry 
form,  dissolve  one  gram  in  100  c.c.  of  96  per  cent  alcohol.  Dilute 
bases  turn  colorless  phenolphthalein  to  a  red  color  and  acids  change 
it  back  to  colorless  condition.  As  a  test  for  acids  and  bases  it  is  much 
more  delicate  than  litmus. 

Phos'phor  us,  a  simple  chemical  element  which  oxidizes  very  readily. 
Yellow  phosphorus  (a  phosphorus  oxide)  must  be  kept  under  water 
and  not  handled  with  bare  fingers  in  the  open  air.  Cut  it  under 
water.  Red  phosphorus  (a  phosphorus  oxide)  is  not  so  dangerous, 
and  ignites  at  260°  C.  Phosphorus  is  used  in  the  manufacture  of 
matches,  and  for  fertilizer  in  the  form  of  phosphoric  acid. 

Piston,  the  sliding  piece  in  the  cylinder  of  an  engine  or  pump.  The  rod 
attached  to  it  is  the  piston  rod.  In  an  engine  the  piston  is  moved  by 
steam  or  other  gas;  in  a  pump  it  is  moved  by  the  force  applied  to  the 
handle  of  the  pump. 

Platinum  electrode,  a  piece  of  sheet  platinum  in  an  apparatus  for 
decomposing  water.  The  electricity  passes  into  the  water  by  one 
electrode  and  leaves  the  water  by  the  other  electrode. 

Pneu  mafic  trough  (nu  mat'ik),  an  open-topped  vessel  with  a  shelf 
in  it  for  supporting  inverted  bottles  full  of  water  in  such  a  way  that  a 
tube  may  be  inserted  for  catching  a  gas.  (See  illustration  on  page  48.) 


GLOSSARY 

Pre  cip'i  tate,   an  insoluble   compound   formed   sometimes   when, 
soluble  compounds  are  poured  together.    If  hydrochloric  acid  is 
to  a  solution  of  lead  nitrate  a  white  precipitate  of  lead  chloride  will 
be  formed. 

Ra'di  um,  an  intensely  radio-active,  metallic  element  found  in  minute 
quantities  in  pitchblend  and  carnotite.  Some  is  found  in  the  state 
of  Colorado.  It  has  the  property  of  giving  off  light,  etc. 

Rare  air,  air  that  weighs  less  per  unit  volume  than  air  at  sea  level,  or 
air  that  is  less  dense  than  some  other  air.  A  cubic  foot  of  air  on  top 
of  a  mountain  three  miles  high  weighs  only  one-half  as  much  as  a 
cubic  foot  of  air  at  sea  level. 

Re  frig  er  a'tion,  a  process  by  which  foods  are  kept  at  a  low  temperature 
so  that  they  do  not  spoil  very  rapidly.  Meat,  eggs,  fruit,  and  vege- 
tables are  often  kept  in  cold  storage  or  refrigerator  rooms. 

Retting,  a  process  of  preparing  flax  plants  by  soaking  them  in  water. 
It  causes  the  soft  parts  of  the  stems  to  decay  and  then  the  fiber  is 
combed. 

Sa  li'va,  the  digestive  fluid  secreted  by  six  small  glands  and  poured  into 
the  mouth  in  large  quantity  while  one  is  eating;  at  other  times  a 
sufficient  amount  is  secreted  to  keep  the  mouth  moist.  It  contains 
an  enzyme,  — ptyalin,  —  which  can  change  starch  to  sugar. 

Saturated  solution,  a  liquid  containing  as  much  of  another  substance 
as  it  can  hold  in  solution.  When  water  has  all  the  dissolved  salt  or 
sugar  that  it  can  hold,  it  is  a  saturated  solution. 

Sed'en  ta  ry,  when  applied  to  a  man,  means  one  who  does  not  take 
much  physical  exercise.  Bookkeepers  and  stenographers  lead  a 
sedentary  life.  They  should  take  exercise  in  the  open  air  when 
possible. 

Seedling,  a  young  plant  in  the  germinating  stage. 

Si'sal,  a  kind  of  hemp  of  which  rope  is  made.  It  grows  in  Mexico  and 
in  Central  America. 

Ster'i  lize,  to  treat  tools  and  substances  in  such  a  way  that  living 
organisms,  disease  germs,  are  killed.  Boiling  water  and  chemicals 
are  used  for  this  purpose. 

Tho  rac'ic  duct  (thoras'ik),  a  tube  just  inside  the  spinal  column.  It 
extends  from  back  of  the  middle  of  the  digestive  organs  to  the  left 
side  of  the  neck,  where  it  connects  with  a  large  vein  coming  down  from 
the  head.  The  digested  fat,  and  lymph  (a  milky-colored  liquid  from 
many  parts  of  the  body)  pass  into  the  blood  through  this  tube. 

Volt,  a  unit  of  electromotive  force.  It  is  an  electromotive  force  which 
will  drive  a  current  of  one  ampere  over  a  conductor  which  has  a  resist- 
ance of  one  ohm. 

Water  sprouts,  branches  which  appear  around  the  base  or  on  large 
limbs  of  trees.  They  should  not  be  left  on  trees  because  they  make 
them  too  bushy,  waste  the  food  of  the  trees,  and  bacteria  diseases 
can  easily  enter  the  trees  through  them. 


424 


GLOSSARY 


Names  of  Some  Common  Chemical  Elements  and  Their  Symbols 


Calcium Ca. 

Carbon C. 

Chlorine Cl. 

Copper Cu. 

Hydrogen H. 

Iodine I. 

Iron Fe. 

Mercury Hg. 


Nitrogen N. 

Oxygen , O. 

Phosphorus P. 

Potassium K. 

Sodium Na. 

Sulphur S. 

Zinc .  .Zn. 


SUGGESTIONS   FOR  TEACHERS 

General  Suggestions.  —  Please  keep  in  mind  that  students  are  being 
taught  and  that  the  subject  matter  must  be  adapted  to  their  capacity 
and  needs.  Study  the  experiences  and  needs  of  the  students  and  make 
the  subject  a  living  one  by  presenting  it  to  them  in  such  a  way  that  they 
will  begin  to  use  it  immediately.  Connect  it  with  their  everyday  life 
by  drawing  on  their  experiences  and  home  environment.  Whenever 
possible  have  the  students  bring  the  material  for  classroom  use,  and 
have  them  prepare  everything  possible.  The  duty  of  the  teacher  is  to 
keep  the  students  busy  at  something  useful. 

The  questions  and  exercises  at  the  close  of  each  chapter  will  give 
some  suggestions  for  detailed  procedure.  Some  detailed  suggestions 
for  the  treatment  of  a  few  chapters  follow: 

Chapter  III.  —  Before  assigning  any  work  in  this  chapter  give  the 
students  some  red  and  blue  litmus  paper  and  have  them  test  many  of 
the  substances  which  they  have  at  home,  arranging  the  compounds  in 
three  columns,  namely: 

(i)  Acids  (2)  Bases  (3)  Neutrals 

Tell  them  that  those  substances  which  turn  blue  litmus  paper  to  a 
red  color  are  acids,  those  which  turn  red  litmus  to  blue  are  bases,  and 
those  which  do  not  affect  either  red  or  blue  litmus  are  neutral  com- 
pounds. 

Have  them  test  such  compounds  as  water,  milk,  lard,  vinegar,  baking 
soda,  soap,  alcohol,  etc. 

Limewater  can  be  made  by  placing  about  one  pound  of  unslaked  lime 
in  four  pints  of  water.  Use  a  tall  vessel  and  shake  well  after  slaking  the 
lime  and  set  it  aside  for  a  day  or  more,  so  that  the  undissolved  lime  can 
settle,  then  pour  off  the  clear  limewater  into  a  bottle  for  future  use. 

A  potash-lye  solution  may  be  made  of  the  lye  purchased  in  grocery 
stores  by  dissolving  it  in  water.  Household  ammonia  and  baking  soda 
may  also  be  obtained  from  the  grocery. 

These  bases  with  vinegar,  sour  milk,  and  fruit  juices  for  acids  will  be 
sufficient  material  for  classroom  demonstration  to  show  the  nature  of 
such  compounds.  If  you  have  an  equipped  laboratory  use  the  chemi- 
cals at  your  disposal,  but  be  sure  that  you  connect  the  work  with  the 
life  of  the  students. 

Have  the  students  make  soap  at  home  and  bring  the  finished  product 
to  school.  Give  them  the  directions  for  making  the  soap  and  supply 
a  small  quantity  of  lye  if  you  have  it. 

Have  the  students  test  their  home  water  to  learn  whether  it  is  hard 


426  SUGGESTIONS   FOR   TEACHERS 

or  soft.    Have  them  find  whether  it  is  cheaper  to  soften  water  with  soap 
or  with  washing  powder,  etc. 

Chapter  IV.  —  Have  each  student  bake  some  biscuits  by  using  the 
baking  chemicals  as  follows: 

(1)  By  using  baking  soda  without  any  acid. 

(2)  By  using  baking  soda  with  sour  milk. 

(3)  By  using  baking  soda  with  vinegar  or  hydrochloric  acid. 

(4)  By  using  baking  powder  with  vinegar  or  sour  milk. 

(5)  By  using  baking  powder  without  any  acid. 

(6)  By  dissolving  the  baking  powder  in  water  and  then  mixing 

the  solution  with  the  material  to  be  baked. 

Have  the  students  bring  their  products  to  school  and  explain  why 
such  different  results  were  obtained. 

Chapter  VI.  —  The  first  assignment  in  this  chapter  should  be  as 
follows: 

(1)  Define  stimulant. 

(2)  Name  some  common  stimulants. 

(3)  Make  a  list  of  all  the  good  effects  which  come  from  their 

habitual  use. 

(4)  Make  a  list  of  the  evil  effects  which  come  from  their  habitual 

use. 

During  the  recitation  have  the  students  freely  discuss  the  topics, 
but  with  the  teacher  always  in  control.  The  teacher  should  present 
additional  facts  and  then  let  the  students  draw  their  own  conclusion. 

Treat  the  subject  of  narcotics  by  the  same  method. 

Chapter  XIX.  —  Let  the  environment  of  the  school  determine  to 
what  extent  you  require  the  students  to  master  this  chapter.  Use 
sufficient  details  to  enable  the  students  to  understand  the  simple  ma- 
chines which  they  have  already  used.  Always  draw  upon  their  experi- 
ences and  use  these  as  a  basis  on  which  to  build.  Have  them  report  on 
where  they  have  seen  levers,  inclined  planes,  pulleys,  etc.,  used.  Let 
them  explain  how  these  machines  were  being  used. 

Chapter  XXXII.  —  Have  the  students  examine  some  soil  and  bring 
some  to  class  for  more  careful  examination.  Have  students  bring  roots 
of  clover  or  similar  plants  and  examine  the  tubercles.  Have  a  student 
make  a  report  to  the  class  on  nitrogen  compounds  used  for  fertilizer. 
Have  them  visit  gardens  and  farms  to  see  how  soil  is  treated  while 
caring  for  plants. 

Chapter  XXXIV.  —  Have  all  students  plant  at  home  such  seeds  as 
beans,  pumpkin  seeds,  corn,  peas,  etc.,  in  soil,  sawdust,  or  sand  to  learn 
how  such  seeds  start  to  grow  and  to  learn  the  necessary  conditions  for 
healthy  germination  of  such  seeds..  In  a  village  or'  country  high  school 
germinating  tests  of  seeds  should  be  made  by  taking  six  grains  from 
various  places  on  an  ear  of  corn  and  placing  them  in  proper  germinating 
conditions.  If  all  six  grains  grow  the  ear  should  be  saved  for  seed. 

To  make  a  seed  germinating  tester,  take  a  box  a  foot  or  more  square 
and  about  two  inches  deep.  Stretch  wires  across  both  ways,  making 
two-inch  squares.  Fill  the  box  with  soil  up  to  the  wires  and  cover  the 


SUGGESTIONS   FOR  TEACHERS  427 

soil  with  a  cloth  by  placing  the  cloth  under  the  wires.  Number  and 
letter  the  squares  on  two  adjoining  sides  respectively.  Then  every 
square  can  be  located  by  using  a  number  and  a  letter.  Take  six  grains 
from  each  ear  of  corn  to  be  tested  and  place  them  in  the  squares  and  at 
the  same  time  place  a  label  composed  of  a  number  and  a  letter  on  each 
ear,  indicating  where  its  six  grains  are.  After  the  tester  has  seeds  in 
each  square,  cover  it  with  damp  cloths  and  keep  them  damp,  also  keep 
the  tester  in  a  warm  room.  Discard  all  ears  that  do  not  give  a  100  per 
cent  test. 

Other  seeds  may  be  tested  the  same  as  corn. 

Chapter  XXXVIII.  —  Have  students  bring  to  class  all  kinds  of  raw 
fruit  and  branches  of  fruit  trees,  and  examine  them  carefully  for  diseases 
and  animal  pests.  Have  them  bring  in  old  fruit  which  dried  on  the 
trees  and  examine  for  brown-rot.  If  this  dried  fruit  (mummies)  shows 
any  development  of  brown  spores  after  it  is  kept  moist  in  a  warm  room 
for  a  week  or  more,  brown-rot  is  present. 

Examine  other  plants  for  diseases  and  pests. 


INDEX 


Accommodation,  optical,  281 
Acetylene  gas,  293 
Acids,  12 

Acetic,  13 

Citric,  12 

Hydrochloric,  13 

Lactic,  12 

Malic,  12 

Nitric,  13 

Sulphuric,  13 
Adenoids,  61 
Aeronauts,  156 
Air,  6,  47,  145,  312 
Air  pumps,  147 
Alcohol,  41,  43,  88,  89 
Algze,  368 
Alkaloids,  41,  419 
Alum,  26 
Ammonia,  14,  169 
Amoeba,  381 
Ampere,  251 
Amphibians,  388 
Animals,  381,  396 
Anther  of  flower,  347 
Apples,  375 
Apple  rust,  373 
Aqueous  humor,  279 
Arsenate  of  lead,  379 
Artificial  gas,  171 
Astigmatism,  285 
Atmosphere,  146 
Atoms,  ii 

Bacteria,  31,  33,  315,  371 
Baking  powder,  25,  26 
Baking  soda,  24,  25,  26 
Bananas,  350,  351 
Barometers,  150,  152 
Bases,  14 
Beans,  335 

Bell,  Alexander  Graham,  268 
Birds,  391 

Block-and-tackle,  192 
Boiling,  85,  138,  226 


Borax,  38 

Bordeaux  mixture,  378,  419 
Boyle's  Law,  165 
Bread,  24,  28,  29 
Breathing,  6,  59,  62,  91 
Brown  rot,  375 
Budding,  354,  355 
Burbank,  Luther,  349 
Buying  food,  130 

Caffeine,  40,  41 

Calcium  chloride,  94 

Calorie,  77 

Calyx,  346 

Cambium,  342 

Cameras,  273 

Camping,  139 

Cankers,  376 

Caramel,  24,  419 

Carbohydrates,  115 

Carbolic  acid,  36,  37 

Carbon,  54 

Carbon  dioxide,  47,  56,  57,  58 

Cattle,  394 

Cedar  apples,  374 

Cells,  of  body,  113 

Cells,  in  parallel,  258;  in  series,  258 

Cellulose,  366 

Centrifugal  pump,  218 

Chalk,  309 

Charcoal,  53,  55 

Chloride  of  lime,  36 

Chloroform,  45 

Chlorophyll,  345 

Cilia,  383 

Climate,  143 

Clothing,  6,  98,  363 

Cocaine,  44 

Cocoa,  41 

Codeine,  44 

Codling  moth,  378 

Coffee,  40,  41 

Cogwheels,  195 

Coke,  56 


430  INDEX 


Colds,  61 

Color  blindness,  284 
Compass,  238 
Compound,  12 
Compression  pump,  221 
Conduction  of  heat,  96 
Convection,  98 
Cooking,  23,  131 
Corn,  336,  361 
Cornea,  279 
Corolla,  346 
Cotton,  363 
Cough  remedies,  45 
Crayfish,  386 
Creosote,  39 
Crystalline  lens,  280 
Cultivation,  321 
Cuttings,  353 

Daniell  cell,  the,  256 

Decay,  52 

Declination,  247 

Dew,  157 

Dew  point,  158 

Dextrin,  23 

Diastase,  27,  337 

Diet,  128 

Diseases,  of  man,  396;  of  plants,  373, 

377 

Disinfectants,  36 
Dispatch  tubes,  224 
Dissolution,  94 
Distillation,  87,  138,  226 
Drainage,  325 
Dry  cell,  263 

Ears,  302,  304 

Earth,  the,  407 

Earth,  a  magnet,  245 

Earthworm,  384 

Eclipse,  409 

Efficiency,  180,  216 

Eggs,  120 

Electric,  bell,  262;    cell,  252;    current, 

250;   lights,  266 
Electrical  units,  251 
Electricity,  248 
Electromagnet,  260 
Electromotive  force,  251 
Element,  12 
Embryo,  348 
Emulsion,  18 

Energy,  67,  176;  law  of,  69 
Engines,  68,  207 


Enzymes,  337 
Erosion,  141,  329,  332 
Evaporation,  10,  92 
Evolution,  174 
Exhaust  pump,  223 
Eye,  279 

Farsightedness,  284 

Fats,  1 1 6 

Fehling's  solution,  122,  420 

Fertilization,  348 

Fertilizer,  320 

Filtration,  139,  226 

Fire  extinguisher,  57,  58 

Fireless  cooker,  108 

Flame,  candle,  291 

Flax,  364 

Flea,  400 

Flower  beds,  324 

Flowers,  346 

Food,  7,  116,  361 

Force,  177 

Force  pump,  221 

Formaldehyde,  37 

Fractional  distillation,  89 

Freezing,  94 

Frog,  389 

Frost,  157 

Fruit,    349;     seedless,    350;     varieties 

of,  34Q 

Fuel,  needs,  124 
Fulcrum,  185 
Fungi,  370,  373 
Furnace,  100,  102 
Fusion,  heat  of,  92 

Gas,  65,  163,  289;  engines,  210;  meter, 

172;    pressure,  163;    pumps,  221 
Germs,  31,  32,  34 
Germination,  337 
Glass,  93,  96,  97 
Glossary,  419 
Gluten,  24,  119 
Glycogen,  116 
Grafting,  354,  356 
Grain,  336 
Gravitation,  69 

Gravity,  66,  177;  cell,  256;  system,  228 
Greenhouse,  96 
Gulf  Stream,  99,  143 

Health,  5,  6,  7 

Heat,  34,  42,  71,  78,  79,  95,  167 

Heat  of  fusion,  92 


INDEX 


431 


Heat  of  vaporization,  84 
Heating  buildings,  95 
Headache,  44,  285 
Hearing,  303 
Helix,  260,  261 
Hemp,  365 
Hog,  394,  401 
Home  selecting,  405 
Hookworm,  402 
Horse,  394 
Horsepower,  197 
Hospitals,  287 
Hot  beds,  325 
House  fly,  396 
Human  body,  112 
Humidity,  158 
Humus,  313 
Hydrogen,  135 
Hygrometer,  158 

Ice,  artificial,  169 
Inclined  plane,  186 
Insects,  378,  385 
Irrigation,  326 
Isobars,  158 
Isotherms,  159 

Japan  current,  99,  143 
Kindling  point,  50 

Laudanum,  44 

Law  of  magnets,  239 

Leaves,  343 

Leclanche  cell,  257 

Lenses,  273 

Lenticels,  346 

Lever,  181 

Lichens,  13 

Lifting  pump,  214 

Light,  272,  412;  artificial,  289 

Lightning,  250;  rods,  249 

Lime,  36 

Limestone,  308 

Lime-sulphur,  3/6 

Linseed  oil,  365 

Liquids,  65 

Liquid  air,  171 

Litmus,  13,  15 

Liver,  116 

Lobsters,  387 

Lodestone,  237 

Machines,  174 

Magnetic,  field,  242,  258;  poles,  246 


Magnetism,  induced,  240 

Magnetizing  steel,  245 

Magnets,  237;  care  of,  244 

Malaria  fever,  399 

Mammals,  393 

Man,  404;  enemies  of,  405 

Manganese  dioxide,  47,  263 

Matches,  51 

Material,  64 

Matter,  64;   law  of,  65;  state  of,  65 

Mechanical  advantage,  179 

Metals,  94,  96 

Meteors,  412 

Meter,  415 

Metric  system,  414 

Milk,  117 

Mineral  foods,  121 

Molds,  31,  370 

Molecules,  10 

Moon,  408 

Morphine,  44 

Mosquitoes,  398 

Mummies,  of  fruit,  375 

Mushrooms,  370 

Natural  gas,  171,  292 
Nearsightedness,  283 
Newton,  Sir  Isaac,  67 
Nicotine,  42,  62 
Nitrogen,  47,  319 
Nutrients,  114,  122 
Nutritive  ratio,  127 

Ohm,  251 
Oil,  289,  292,  365 
Opium,  42,  44 
Oranges,  350 
Osmosis,  339 
Ovary,  347 
Overshot  wheel,  200 
Ovules,  347 
Oxidation,  49,  52 
Oxygen,  47,  48,  49 

Paint,  39 
Paper,  336 
Paramecium,  382 
Parasites,  370 
Pasteurizing,  34 
Pear  blight,  376 
Pelton  wheel,  201 
Petroleum,  90 
Phenolphthalein,  16,  422 
Phosphorus,  51 


432 

Pineapples,  350,  351 

Pistil,  347 

Planets,  410 

Plants,  335,  352,  361,  367,  368,  373 

Polarization,  254,  255 

Pollen,  347 

Pollination,  348 

Pond  scum,  369 

Potassium  chlorate,  47,  51 

Potatoes,  362 

Potential,  251,  253 

Power,  196 

Pressure,  148 

Primitive  man,  100,  404 

Protein,  118 

Protoplasm,  339 

Protozoa,  381 

Pruning,  357 

Pulleys,  loo 

Pumping  system,  228 

Pumps,  213 

Pupil  of  eye,  279 

Purifying  water,  138,  226 

Radiation,  95 
Rain,  157 
Rainbow,  274 
Rat,  400 

Refrigeration,  168,  423 
Reptiles,  390 
Reservoir,  230 
Retina,  280 
Rice,  363 

Right-hand  rule,  259 
Rock,  308 
Roots,  338,  352 
Ropes,  365 
Rusts,  373 

Salts,  20,  94 

San  Jose  scale,  377 

Saprophytes,  370 

Screw,  189 

Seeds,  335,  352 

Shooting  stars,  412 

Siphon,  213 

Smokers,  43 

Snakes,  300 

Snow,  98,  157 

Soap,  16,  17,  18 

Soft  drinks,  40 

Soil,  305;  care  of,  321 

Solid,  65 

Solvent,  140 


INDEX 


Soothing  sirups,  45 

Sound,  294 

Specific  heat,  77,  78 

Spectrum,  274 

Spirogyra,  369 

Spontaneous  combustion,  50 

Spores,  35,  369,  374 

Stamens,  347 

Standpipe,  229 

Starch,  115 

Stars,  411 

Steam,   n,   104;    engines,  207;    gauge, 

164;    heating,  104 
Stems  of  plants,  340 
Stigma,  347 
Stimulants,  40,  41 
Stomach,  7,  103 
Stomata,  344 
Stove  for  heating,  101 
Style  of  flowers,  347 
Success,  6 

Sugar,  54,  115;  cane,  362 
Sulphur,  36,  37 
Sun,  408 

Tapeworm,  401 
Tea,  40,  41 
Telegraph,  262 
Telephone,  268,  270 
Temperature,  76 
Theine,  41 
Theobromine,  41 
Thermometers,  72 
Thermos  bottle,  no 
Tinder,  51 
Toad,  389 
Tobacco,  42.  62 
Transformer,  electrical,  266 
Transplanting,  357 
Trees,  357,  359 
Trichina,  402 
Turbine  wheel,  202 
Twines,  365 

Undershot  wheel,  201 

Vacuole,  381,  383 
Varnish,  39 
Ventilation,  63,  100 
Vibrations,  295 
Vision,  281 
Vitreous  humor,  280 
Vocal  cords,  300 


INDEX 


433 


Voice,  301 

Volt,  251,  252,  423 

Washing  soda,  20 

Water,  6,  19,  20,  82,  92,  121,  134,  310; 

power,    199;    pressure,    230;     supply, 

225 

Water  and  disease,  226 
Water  and  forests,  233 
Waterfall,  value  of,  203 
Watt,  unit  of  power,  198 
Weather  Bureau,  160;  maps,  160 
Wedge,  1 88 
Wells,  224 


Wheat,  361;  rust,  373 
Wheel-and-axle,  194 
Wind,  99 
Windlass,  194 
Windmills,  204 
Wireless  apparatus,  265 
Wood  alcohol,  89 
Work,  denned,  178 
Worms,  384 

Yeast,  24,  27,  28,  371 
Yellow  fever,  400 

Zygospore,  369 


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For  younger  classes;  the  main  things  to  know  in  order  to  write  English  cor- 
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About  2500  problems  covering  both  elementary  and  advanced  work. 

Boynton,  Morse  and  Watson's  Manual  of  Chemistry 50 

A  laboratory  guide  with  detailed  directions  for  90  experiments. 

Cheston,  Gibson  and  Timmerman's  Physics 1.25 

Modern  throughout  —  especially  in  electricity,  light,  and  color. 

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A  well-balanced  course,  with  a  new  presentation  of  mechanics. 

Fisher  and  Patterson's  Elements  of  Physics 75 

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An  introductory  course,  original  in  its  treatment  of  basic  analysis. 

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Miller's  Progressive  Problems  in  Physics 64 

About  1500  graded  problems  of  practical  import. 

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Orndorff's  Laboratory  Manual  in  Organic  Chemistry 40 

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Remsen's  Organic  Chemistry 1.40 

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Roberts's  Stereo-Chemistry 1.00 

Shepard's  Inorganic  Chemistry 1.20 

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